By Steve Olafson
OKLAHOMA CITY, April 30 (Reuters) - A tornado hit a small Oklahoma town on Monday, knocking out power to the community of 1,000 residents and damaging a farm just two weeks after a tornado elsewhere in the state killed at least six people, the National Weather Service said.
No injuries were immediately reported in Monday night's twister in Medford, but much of northern Oklahoma was placed under tornado watch through the night, and flash flood warnings were issued due to heavy rains the past two days, said Forrest Mitchell of the National Weather Service in Norman, Oklahoma.
In nearby Deer Creek, Oklahoma, authorities began evacuating residents late Monday when a leak was discovered in a 30,000-gallon tank of volatile anhydrous ammonia at the farmer's grain co-op, a spokeswoman for the Grant County Sheriff's Department said.
It was unclear if the leak was caused by the tornado, high winds and hail that swept through the area, said Shari Payne of the sheriff's department.
The U.S. tornado season started early this year, with twisters already blamed for 63 deaths in 2012 in the Midwest and South, raising concerns that this year would be a repeat of 2011, the deadliest tornado year in nearly a century.
Monday's tornado came about two weeks after a twister hit the town of Woodward, also in northwest Oklahoma, killing at least six people.
Some 550 people died in tornadoes last year, including 316 killed in an April outbreak in five Southern states, and 161 people in Joplin, Missouri, the following month. (Editing by Cynthia Johnston and Lisa Shumaker)