SYDNEY (AP) — The cruise ship railing over which an Australian couple fell into the ocean was higher than industry regulations required and was designed to prevent accidental falls, a spokeswoman for the cruise company said Friday as an intense search continued for the missing passengers.

Paul Rossington, a 30-year-old paramedic, and his 26-year-old girlfriend Kristen Schroder, both from the town of Barraba in New South Wales state, were discovered missing Thursday morning after the Carnival Spirit docked at Sydney's Circular Quay at the end of a 10-day journey, New South Wales Police Superintendent Mark Hutchings said.

Stephen Leahy, head of Westpac Life Saver Rescue Helicopters, said that if the couple fell accidentally, they could have survived, noting that the ocean was calm and fairly warm, and describing Rossington, a paramedic for the state ambulance service, as very fit. "He has a very good understanding ... of survival techniques and his level of fitness will help him," Leahy told Australian Broadcasting Corp. "He'll also be able to help his partner. The chances of two young people surviving are very, very good, and certainly from our perspective, we haven't given up hope."

Surveillance camera footage showed the couple was outside their cabin when they fell more than 20 meters (65 feet) from the ship's mid deck Wednesday night, Hutchings said. At the time, the ship was about 120 kilometers (65 nautical miles) off the coast of Forster, a city 300 kilometers (185 miles) north of Sydney.

Carnival Spirit is owned by Miami-based Carnival Corp., the world's largest cruise operator. Carnival Corp.'s representative in the South Pacific region, Ann Sherry, chief executive of Carnival Australia, said the railing over which the couple fell was 5 centimeters (2 inches) higher than industry safety regulations mandate.

"It's designed really to prevent accidental tripping" overboard, she told reporters.

"We want to make sure that it's not possible for people to fall overboard or to trip and fall overboard ... so I think it would be highly unlikely, but again, in this case, the police are conducting a full investigation," she said.

Rescue officials searched through the night with heat-seeking infrared equipment, but had not found the couple as of Friday afternoon, police said.

"I do have grave concerns for them.... whilst we hold out some hope, the hope is fading, unfortunately," Hutchings told reporters.

Investigators were having the surveillance video enhanced in a bid to determine whether Rossington and Schroder jumped or fell by accident. The video shows the pair went over the railing around the same time, with a brief pause between them, Hutchings said. It is not clear from the footage who went overboard first.

Police were also questioning family, friends and passengers in a bid to find out what happened. "The footage alone won't tell the whole story," Hutchings said.

No life preservers were missing from the ship, Hutchings said. A missing life preserver might have indicated that one of the missing passengers had attempted a rescue.

The ship has around 600 surveillance cameras that are constantly monitored, although no one reported seeing the fall at the time. Sherry defended the level of monitoring of passengers aboard the ship that allowed the couple's fall to go unnoticed. At least four people were monitoring the ship's surveillance cameras at any time, she said.

The night Rossington and Schroder vanished, the video surveillance staff was busy watching the public areas of the ship, she said.

"It was the last night of a cruise," Sherry said. "Virtually everybody else was in the public spaces on the ship, and they're the areas that we focus on in those times."

Andrea Hayward-Maher, spokeswoman for the Australian Maritime Safety Authority, which is coordinating the search, said five airplanes and a helicopter were searching a 700-square-kilometer (200-square-nautical mile) area of sea 110 kilometers (70 miles) east of Forster. She said search conditions were good.

The couple and seven of their family and friends were among 2,680 passengers on a South Pacific cruise. The ship's last stop was Mare Island in New Caledonia, which it left on Monday, bound for Sydney.

The emergency is the latest high-profile problem for Carnival Corp.

Last year, the Costa Concordia ran aground off the coast of Italy, killing 32 people. Also last year, the Costa Allegra caught fire and lost power in the Indian Ocean, leaving passengers without working toilets, running water or air conditioning for three days. Costa is a division of Carnival Corp.

In February, passengers aboard the Carnival Triumph spent five days without power in the Gulf of Mexico after an engine-room fire disabled the vessel. Those on board complained of squalid conditions, including overflowing toilets and food shortages.

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  • The sun sets as the cruise ship Carnival Triumph is towed into Mobile Bay near Dauphin Island, Ala., Thursday, Feb. 14, 2013. (AP Photo/Dave Martin)

  • The cruise ship Carnival Triumph is towed up the Mobile River in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/Dave Martin)

  • The cruise ship Carnival Triumph is pushed towards the cruise terminal along the Mobile River in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/Dave Martin)

  • The cruise ship Carnival Triumph is towed up the Mobile River in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/Dave Martin)

  • People watch from their balconies aboard the Carnival Triumph after it was towed to the cruise terminal in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/G M Andrews)

  • People watch from their balconies aboard the Carnival Triumph after it was towed to the cruise terminal in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/John David Mercer)

  • Passengers aboard the Carnival Triumph walk along the deck before leaving the ship in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/Dave Martin)

  • Carnival Triumph Arrives

    People watch from their balconies and hold up signs aboard the Carnival Triumph after it was towed to the cruise terminal in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/AL.com, Mike Brantley)

  • Passengers of the Carnival Triumph walk to their buses after docking at the cruise terminal in Mobile, Ala., Thursday, Feb. 14, 2013. (AP Photo/Dave Martin)

  • Passengers from the disabled Carnival Triumph cruise ship arrive by bus at the Hilton Riverside Hotel in New Orleans, Friday, Feb. 15, 2013. (AP Photo/Gerald Herbert)

  • Passengers from the disabled Carnival Triumph cruise ship arrive by bus at the Hilton Riverside Hotel in New Orleans, Friday, Feb. 15, 2013. (AP Photo/Gerald Herbert)

  • This undated photo provided by passenger Don Hoggatt, of Dallas, shows makeshift tents on the deck of the Carnival Triumph cruise ship for people to spend the day in and sleep in to escape the stench from the lower decks of the disabled ship.The Triumph arrived late Thursday, Feb. 14, 2013, in Mobile, Ala., after an engine-room fire left the ship powerless off Mexico last weekend. (AP Photo/Don Hoggatt)

  • This undated photo provided by passenger Don Hoggatt, of Dallas, shows the tent city built on the Lido deck of the Carnival Triumph cruise ship for people to spend the day or night in to escape the stench from the lower decks of the disabled ship. The Triumph arrived late Thursday, Feb. 14, 2013, in Mobile, Ala., after an engine-room fire left the ship powerless off Mexico last weekend. (AP Photo/Don Hoggatt)

  • This undated photo provided by passenger Don Hoggatt, of Dallas, shows covered urinals and bagged trash cans for passengers to use in one of the bathrooms aboard the Carnival Triumph cruise ship which became disabled after an engine-room fire left the ship powerless off Mexico last weekend. The Triumph arrived late Thursday, Feb. 14, 2013, in Mobile, Ala., after an engine-room fire left the ship powerless off Mexico last weekend. (AP Photo/Don Hoggatt)

  • The cruise ship Carnival Triumph is moored at a dock in Mobile, Ala., Friday, Feb. 15, 2013. The ship, which docked Thursday in Mobile after drifting nearly powerless in the Gulf of Mexico for five days, was moved Friday from the cruise terminal to a repair facility. (AP Photo/Dave Martin)

  • In this image released by the U.S. Coast Guard on Feb. 11, 2013, a small boat belonging to the Coast Guard Cutter Vigorous patrols near the cruise ship Carnival Triumph in the Gulf of Mexico, Feb. 11, 2013. (AP Photo/U.S. Coast Guard- Lt. Cmdr. Paul McConnell)

  • In a Feb. 12, 2013 photo provided by the U.S. Coast Guard, the tugs Resolve Pioneer and Dabhol, left, tow and steer the 893-foot Carnival Triumph cruise ship in the Gulf of Mexico. (AP Photo/U.S. Coast Guard, Ensign Chris Shivock)

  • In this image released by the U.S. Coast Guard on Feb. 11, 2013, the Coast Guard Cutter Vigorous patrols near the cruise ship Carnival Triumph in the Gulf of Mexico, Feb. 11, 2013. T(AP Photo/U.S. Coast Guard- Lt. Cmdr. Paul McConnell)

  • This July 27, 1999 handout file photo provided by Carnival Cruise Lines shows the MS Carnival Triumph departing New York harbor, on her inaugural voyage. Carnival Cruise Lines said Sunday an engine room fire had disabled the cruise ship Triumph about 150 miles off the Yucatan Peninsula with 3,143 passengers and 1,086 crew members on board. (AP Photo/Carnival Lines, Andy Newman, File)

  • Cruise Ship Loses Power In Gulf Of Mexico

    In this handout from the U.S. Coast Guard, the cruise ship Carnival Triumph sits idle February 11, 2013 in the Gulf of Mexico. (Photo by Paul McConnell/U.S. Coast Guard via Getty Images)