By Ruma Paul

DHAKA, Sept 23 (Reuters) - More than 100 Bangladeshi garment factories were forced to shut on Monday as thousands of workers protested to demand a $100 a month minimum wage and about 50 people were injured in clashes, police and witnesses said.

Garments are a vital sector for Bangladesh and its low wages and duty-free access to Western markets have helped make it the world's second-largest apparel exporter after China.

But the $20 billion industry, which supplies many Western brands, has been under a spotlight after a series of deadly incidents including the collapse of a building housing factories in April that killed more than 1,130 people.

Workers took to the streets for a third day on Monday, blocking major roads and attacking some vehicles in the Gazipur and Savar industrial zones, on the outskirts of the capital, Dhaka.

At least 50 people, including some policemen, were injured, witnesses and police said, as police fired teargas and rubber bullets, and workers responded by throwing broken bricks.

Some workers also vandalised factories, witnesses said.

"We had to take harsh actions to restore order as the defiant workers would not stop the violence," an Gazipur police officer said.

The monthly minimum wage in Bangladesh is $38, half what Cambodian garment workers earn.

The government is in talks with unions and factory owners on a new minimum wage.

Bangladesh last increased its minimum garment-worker pay in late 2010 in response to months of street protests, almost doubling the lowest pay.

Recently, factory owners offered a 20 percent pay rise which workers refused, calling it "inhuman and humiliating".

"We work to survive but we can't even cover our basic needs," said a protesting woman worker.

The recent string of accidents has put the government, industrialists and the global brands that use the factories under pressure to reform an industry that employs four million and generates 80 percent of Bangladesh's export earnings.

The April 24 collapse of Rana Plaza, a factory built on swampy ground outside Dhaka with several illegal floors, ranks amongst the world's worst industrial accidents and has galvanized brands to look more closely at their suppliers.

This month, a group of retailers and clothing brands failed to establish compensation funds for the victims of Bangladesh factory disasters, as many companies that sourced clothes from the buildings decided not to take part in the process.

Very low labour costs and, critics say, shortcuts on safety, makes the country of 160 million the cheapest place to make large quantities of clothing, with 60 percent of clothes going to Europe and 23 percent to the United States. (Editng by Robert Birsel)

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  • Bangladeshi garment workers set fire to furniture from a police control room during a protest against the collapse of an eight-story building that housed several garment factories and poor working conditions of the employees, in Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh took into custody five people in connection with the collapse of a shoddily-constructed building that collapsed this week, as rescue workers pulled out 19 survivors out of the rubble on Saturday and vowed to continue as long as necessary to find others despite fading hopes. (AP Photo/A.M. Ahad)

  • Bangladeshi policemen walk after chasing garment workers protesting against the collapse of an eight-story building that housed several garment factories and their employees, in Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh took into custody five people in connection with the collapse of a shoddily-constructed building that collapsed this week, as rescue workers pulled out 19 survivors out of the rubble on Saturday and vowed to continue as long as necessary to find others despite fading hopes. (AP Photo/A.M. Ahad)

  • A Bangladeshi Muslim rescue worker prays on the rubble of a building that collapsed Wednesday in Savar, near Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh arrested two owners of a garment factory in a shoddily-constructed building that collapsed this week, killing at least 324 people, as protests spread to a second city Saturday with hundreds of people throwing stones and setting fire to vehicles. (AP Photo/Kevin Frayer)

  • A girl cries for her missing mother at the site of the garment building factory that collapsed Wednesday in Savar, near Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh took five people into custody in connection with the collapse of a shoddily-constructed building this week, as rescue workers pulled 19 survivors out of the rubble on Saturday and vowed to continue as long as necessary to find others despite fading hopes. (AP Photo/Wong Maye-E)

  • Women carry portraits of missing relatives at the site of the garment factory building that collapsed Wednesday, in Savar, near Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh took five people into custody in connection with the collapse of a shoddily-constructed building this week, as rescue workers pulled 19 survivors out of the rubble on Saturday and vowed to continue as long as necessary to find others despite fading hopes. (AP Photo/Ismail Ferdous)

  • A man watches while rescue workers search for survivors at a garment factory building that collapsed Wednesday in Savar, near Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh took five people into custody in connection with the collapse of a shoddily-constructed building this week, as rescue workers pulled 19 survivors out of the rubble on Saturday and vowed to continue as long as necessary to find others despite fading hopes.(AP Photo/Ismail Ferdous)

  • A Bangladeshi man holds a picture of a relative missing in a building that collapsed Wednesday hold pictures of loved ones at a makeshift morgue in a schoolyard in Savar, near Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh arrested two owners of a garment factory in a shoddily-constructed building that collapsed this week, killing at least 324 people, as protests spread to a second city Saturday with hundreds of people throwing stones and setting fire to vehicles. (AP Photo/Kevin Frayer)

  • A Bangladeshi rescue worker directs others as they search in the rubble of a building that collapsed Wednesday in Savar, near Dhaka, Bangladesh, Saturday, April 27, 2013. Police in Bangladesh arrested two owners of a garment factory in a shoddily-constructed building that collapsed this week, killing at least 324 people, as protests spread to a second city Saturday with hundreds of people throwing stones and setting fire to vehicles. (AP Photo/Kevin Frayer)

  • Relatives mourn a victim at the site where an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. The building collapsed near Bangladesh's capital Wednesday morning, killing dozens of people and trapping many more in the rubble, officials said. (AP Photo/ A.M. Ahad)

  • People and rescuers gather after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • People and rescuers gather after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescuers assist an injured woman after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescue workers carry a victim's body after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescue workers look for survivors after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • A man who was trapped in an collapsed eight-story building housing several garment factories is reccued in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescue workers pull a woman out from the rubbles after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescue workers and people look for survivors after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Relatives mourn a victim at the site after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescuers carry a woman after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescue workers carry a young victim's body after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. Dozens were killed and many more are feared trapped in the rubble. (AP Photo/ A.M. Ahad)

  • Rescue workers use pieces of clothes to bring down a survivor after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. The building collapsed near Bangladesh's capital Wednesday morning, killing dozens of people and trapping many more in the rubble, officials said. (AP Photo/ A.M. Ahad)

  • A man who was trapped in an eight-story building housing several garment factories is rescued after the structure collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. The building collapsed near Bangladesh's capital Wednesday morning, killing dozens of people and trapping many more in the rubble, officials said. (AP Photo/ A.M. Ahad)

  • Rescue workers use clothes to bring down survivors and bodies after an eight-story building housing several garment factories collapsed in Savar, near Dhaka, Bangladesh, Wednesday, April 24, 2013. The building collapsed near Bangladesh's capital Wednesday morning, killing dozens of people and trapping many more in the rubble, officials said. (AP Photo/ A.M. Ahad)