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Several mobile homes in the Hawthorne Hills subdivision in Deland, Fla., seen here, were destroyed in the storms. ((Peter Bauer/Daytona Beach News-Journal/Associated Press))

U.S. President George W. Bush signed a declaration on Saturday to provide disaster assistance for storm-ravagedcentral Florida, where tornadoes are blamed for at least 20 deaths.

A day after the storms sweptthroughSumter, Lake, Volusia and Seminole counties, the U.S. governmentdesignated the region a disaster zone.

Thousands of people had to spend the night in shelters after the twisters struck between 3 and 4 a.m. Friday, uprooting and shredding their homes.

The U.S. National Weather Service says it now believes as many as nine tornadoes may have touched down, NBC reporter Kerry Sanders told CBC News on Saturday. He was in the community of Lake Mack,where the largest of the twisters, an F3, struck, killing at least 13 people. The highest level is F5.

Many had little warning of the severe weather. Thosewho heard reports on their emergency weather radioswere best prepared, Sanders said.

"They grabbed cushions off the sofa, they went into the hallways, they went intoareas where there would be some structure. In one case, a house imploded onto a family of four, who survived by taking shelter in the bathroom."

Few Florida homes have basements because of the high water table. Often peopleshelter in their bathrooms, where the plumbinghelps to anchor the room to the foundation.

Emergency officials in Florida say it could take days to determine just how many people died.The search continued Saturday for thosebelievedtrapped in the rubble of their homes.

Florida Gov. Charlie Crist toured the damagewithFederal Emergency Management Agency Director David Paulison.

FEMA trailers with supplies and materials were expected to arrive in the area as early as Saturday.

Windsestimated at240-255 km/hpicked up one tractor-trailer rig and slammed it down on top of another one. A church in Lady Lake built to withstand a Category 4 hurricane was destroyed.

According to one preliminary estimate, the storm damaged 500 properties and caused around $80 million US worth of damage.

It was the second-deadliest combination of thunderstorms and tornados in the state's history.Similarstorms that tore throughcentral Floridakilled 42 people in1998.