A line of thunderstorms that brought heavy flooding and tornados to Mississippi and Tennessee over the weekend left at least 15 people dead, officials said.

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. Emergency officials sought help from the state's Army National Guard, and urged people to stay off roads and interstate highways turned into raging rivers.

Tennessee officials have confirmed 11 deaths. At least three people are missing after getting swept away by flood waters, and one of them is presumed dead by the Tennessee Emergency Management Agency, which would bring the death toll to 12.

Bredesen said he expects to ask for federal disaster designation.

TEMA spokesman Jeremy Heidt confirmed that one person died around 4 a.m. local time Sunday in a possible tornado near Pocahontas, east of Memphis. No further details were available. Tennesse officials had earlier said as many as eight people died before reducing the death toll to six.

Meanwhile, National Guard and Tennessee Highway Patrol helicopters with hoisting capabilities were on standby to rescue people from the floodwaters that covered city streets and left cars stranded on interstate highways turned into rivers.

In northern Mississippi, officials said a man died after his car was submerged under flood waters. Two people died in a mobile home that "looks like you stuck about four sticks of dynamite on it and it just disappeared," said Coroner John Riles.

County Emergency Management coordinator David Shaw said one person was killed in the town of Abbeville, where 15 or 20 houses were damaged by strong winds.

A line of strong thunderstorms Saturday dumped at least 10 inches (25 centimeters) 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, which could stymie rescuers trying to reach all of the far-flung areas that have been affected.

Some areas were hit by 13 inches (33 centimeters) of flash flooding on Saturday, and the same was expected on Sunday, Browning said.

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Associated Press Writers Kristin Hall in Nashville and Andrew Demillo in Scotland, Arkansas, contributed to this story.