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Towns in the Nashville area were the hardest hit, with at least seven deaths reported north-east of the city.

The storms uprooted trees, overturned cars and knocked out power to thousands of homes, authorities said.

A series of tornadoes across central US last Sunday left 28 people dead, including 24 in west Tennessee.

'Levelled'

Steven Davis, who lives in Gallatin about 24 miles (40km) north-east of Nashville, said he ran to a neighbour's house to take shelter.

"When the tornado came through, the roof was off just like that," Mr Davis said. "Our neighbourhood is levelled."

Nashville mayor Bill Purcell told Reuters news agency cars "were tossed around", though the city appeared to have escaped major damage.

By coincidence, emergency workers and volunteers had been taking part in a series of drills, simulating several disaster scenarios.

"We were all highly mobilised because of this exercise," Mr Purcell said.

Nine of the deaths occurred in Sumner County and the other three were in Warren County, emergency officials said.

More tornadoes

Tornadoes were also reported in the Nashville-area towns of Goodlettsville, Hendersonville and Ashland City, and in Holladay, about 90 miles (145km) west of Nashville.

With many communications links downed, emergency services struggled to assess the full scale of the damage.

At least 60 people were admitted to hospitals in the Nashville area.

The number of tornadoes in the US has risen dramatically in the first part of 2006, according to the National Weather Service's Storm Prediction Centre.