WINONA, MINN. -- Flooding of potentially historic proportions swept across the southeastern boot of Minnesota on Sunday, killing at least six people, displacing hundreds and washing away roads, railroad tracks and homes.

More rain was expected overnight, today and into this week, threatening even more destruction and compounding the misery for thousands who fled their ruined and water-logged homes for higher ground.

Some of the preliminary and unofficial rainfall totals reported to the National Weather Service could exceed the Minnesota single-day rainfall record of 10.84 inches set at Fort Ripley on July 22, 1972. One observer near the Winona County town of Witoka reported 17 inches Saturday into Sunday.

"It's been to the point of overwhelming," said Dave Belz, deputy director of emergency management for Winona County.

Just north of Witoka, two people died after they were the second vehicle to plunge into a 25-foot pit after a road had washed away, officials said.

The rain started about 11 p.m. Saturday and continued through the night, swamping Hwy. 17, just north of Witoka, said Bob Reinert, Winona County administrator.

South of Stockton, one of the hardest-hit communities, two people drowned on County Hwy. 23 after their car was "washed off the road and the ensuing current carried the vehicle away," Reinert said.

Two men also were killed in separate flood-related incidents on Houston County roads. By Sunday night, authorities identified the victims as David T. Blackburn of Spring Grove, Minn., and David R. Ask, of Houston, Minn. Blackburn died in La Crescent Township; Ask in Mound Prairie Township.

Earlier in the evening, authorities had mistakenly reported that the person who died in La Crescent Township was a man from La Crosse, Wis. That man and his son had been stuck in Hokah overnight Saturday and had been out of contact with relatives. They returned to La Crosse safely Sunday afternoon.

Belz said authorities are checking with emergency shelters in an attempt to locate several people who are still missing.

County officials won't begin assessing damage until today.

"We've barely gotten out of rescue mode," Belz said.

By Sunday afternoon, the National Guard had sent 240 soldiers and two helicopters to Winona and the surrounding area to help with security.

Gov. Tim Pawlenty visited the region and declared a state of emergency in six counties: Winona, Wabasha, Fillmore, Houston, Steele, and Olmsted.

Ten state and U.S. highways in the area were closed at times Sunday due to water, mudslides and damage. Drivers should expect to encounter some closures today.

The flooding also led Amtrak to put Twin Cities-bound passengers from points east on buses instead of trains. Riders were expected to arrive almost an hour after their scheduled arrival.

"You can't believe the washouts and the mudslides," said Shirley Van Gundy, 73, who grew up along the Root River and now lives in Houston, a town of about 1,000 residents that was evacuated Sunday afternoon. "It's all over. I know what floods are, and this is the worst."

Because of the topography -- rolling farmland and limestone bluffs -- southeastern Minnesota and southwestern Wisconsin are particularly prone to flash flooding. Heavy rain from uplands to low areas can convert streams and rivers into thundering torrents.