At least 11 people were killed in Tennessee and four in northern Mississippi by a line of storms that brought heavy rain and tornadoes to the region over the weekend.

More rain and storms swept the region Sunday as emergency officials in Tennessee sought help from the state's Army National Guard, and urged people to stay off roads and interstate highways that had turned into raging rivers.

At a Sunday news conference, Tennessee Gov. Phil Bredesen said it will likely be days before floodwaters recede enough to thoroughly assess the damage to roads and bridges.

Tennessee officials have confirmed 11 deaths. There is likely a 12th victim, but a body has not been recovered, Tennessee Emergency Management Agency officials said.

Bredesen said he expects to ask for federal disaster designation.

Earlier Sunday, TEMA asked for the state's National Guard to help with rescue operations.

Agency spokesman Jeremy Heidt confirmed that one person died early Sunday in a tornado near Pocahontas, about 112 kilometres east of Memphis. The other deaths in Tennessee were all due to flooding, TEMA said.

Three people in Mississippi were killed when tornadoes hit their homes and a fourth died after he drove into flood waters.

A spokeswoman at the National Weather Service said it was too early to say if tornadoes had caused the damage in Mississippi.

More rain expected

A line of strong thunderstorms Saturday dumped at least 25 centimetres of rain on Memphis and produced tornadoes and hail along the Mississippi River Valley in Mississippi, Arkansas, Missouri, Kentucky and northward.

The forecast called for more rain through the day Sunday.

Some areas were hit by 33 centimetres of flash flooding on Saturday, and the same was expected on Sunday, Browning said. "This thing is not going to be over this weekend by any means," he said.

The weekend deaths came on the heels of a tornado in Arkansas that killed a woman and injured about two dozen people Friday.

The southwestern part of Tennessee was extremely hard hit, with several Memphis-area streets declared impassable.

Corey Chaskelson, a meteorologist with the National Weather Service, said a levee had been breached along the Big Creek River in Millington, north of Memphis. He said 1.2 to 1.5 metres of water had flooded 200-300 homes at the Naval Support Activity base in Millington.

Emergency officials in Shelby County said hundreds of homes were being evacuated due to high water, including those at a navy base. A federal prison was also evacuated.