By Carey Gillam

OVERLAND PARK, Kansas (Reuters) - Rescue crews used dogs and flashlights to comb piles of debris that once were homes and businesses in Greensburg, Kansas, on Sunday, in a meticulous search for survivors of a killer tornado.

At least eight people died when the twister hit the farming community on Friday night and another was killed in nearby Stafford County. At least 50 people were injured, some critically, authorities said.

Thirty people were rescued from Greensburg's crumbled hospital and authorities believed it was likely that more survivors, and possibly more victims, would be discovered.

"There is the potential of others still being buried in the rubble, people being trapped in basements," Kansas Emergency Management spokeswoman Sharon Watson said. "The focus is on covering a large area as fast as possible."

Some 90 percent of the businesses and homes in Greensburg, a town of about 1,800 people, were damaged or destroyed when the mile-wide tornado and winds of 165 mph roared through.

Watson said assessment teams were to start trying to gauge the cost of the damage during the day.

President George W. Bush declared the community a major disaster area and ordered federal aid to supplement state and local recovery in Kiowa County, which includes Greensburg.

"Our hearts are heavy for the loss of life in Greensburg, Kansas," Bush said after attending church in Washington. "I'm confident this community will be rebuilt."