(Reuters) — Police were turning residents away from Washington, Ill., on Monday morning, the day after a series of tornadoes pounded the Midwest, killing six people across the state and flattening much of the city of 15,000 people.

Bits of American flags and insulation from destroyed homes clung to trees that had been stripped of most of their branches and remaining leaves by the Washington twister. Spawned by a fast-moving storm system, the tornado had winds of up to 200 miles per hour.

The storm, which killed one person in Washington, destroyed 250 to 500 houses in that city, said Mayor Gary Manier. He said authorities were keeping evacuated residents away out of concern that the remaining structures were dangerously unstable.

"I know it's frustrating for people," Mr. Manier said amid piles of rubble left by the storm. "I'd be frustrated. I'd want to be looking for pictures."

The storm killed three people in Massac Country, Ill., two in Washington County, Ill., and one in the city of Washington, in Tazewell County, Ill., said Patti Thompson of the Illinois Emergency Management Agency. It produced about 80 tornadoes, according to the National Weather Service.

The tornadoes leveled scores of homes and demolished entire neighborhoods. The National Weather Service confirmed preliminary EF-4 tornado damage in Washington County in southern Illinois, with winds of 166 to 200 mph.

Nancy Rampy, 62, said she fled to her basement when she heard the storm sirens go off on Sunday.

"It got real calm, and I knew that was bad because I've been in a tornado before. And then I heard what sounded like 12 trains, just roaring down the tracks, and it just wouldn't stop. It just kept coming and coming," Ms. Rampy said. "I ran to the basement, sat in the basement with my flashlight in the dark, and just prayed, 'Let it be over soon.'"

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Ms. Rampy's house was spared, she said, as she headed into work at a Chevrolet dealership a few blocks from the area that had been destroyed.

The unusual late-season storms moved dangerously fast, tracking east at 60 mph, with the bulk of the damage spanning about five hours, Ms. Thompson said. Remnants of the storm brought rain and wind to the northeastern United States on Monday morning.

The storm knocked down power lines across the Midwest, and power companies reported that some 800,000 homes and businesses were without electricity on Monday morning. Michigan had the largest number of outages, with Illinois, Indiana, Ohio, Missouri, West Virginia and Pennsylvania also feeling the storm's aftermath.

Little was left standing in parts of Washington on Monday morning.

U.S. Rep. Aaron Schock, R-Ill., whose district includes Washington, said there is an area where there is not much left standing. "It looks like someone vacuumed up the neighborhood."

"The good news is the tornado warning system worked, so there wasn't a lot of loss of life," Rep. Schock said. "These people knew what was coming, and they were smart and took cover."

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Mr. Manier said that besides the one death, about 60 people had been injured in Washington. One factor that worked to the town's advantage was that many residents had been in churches when the storms hit, he said.

Two people, an 80-year-old man and his 78-year-old sister, were killed in Washington County, about 200 miles south of Peoria, county Coroner Mark Styninger said.

Three others were killed in Massac County, Ill., on the Kentucky border, where a tornado devastated several neighborhoods, emergency officials said.

The American Red Cross worked with emergency management officials to set up shelters and provide assistance.

In neighboring Kentucky, the storm system damaged several homes in the western part of the state, ripping shingles and gutters from roofs, scattering tree limbs and downing power lines. But no one died and no injuries were reported, according to Kentucky Emergency Management spokesman Buddy Rogers.

"We literally dodged a bullet," he said. "When you look across the river (into Illinois), there are places that are just wiped out. But we're in good shape."