Tens of thousands are without power and some people homeless after the freak weather moved through the state.
Tornadoes have killed at least 22 people and destroyed dozens of buildings in Tennessee – including causing severe damage in downtown Nashville.
The twisters toppled power lines and trees and ripped off roofs, causing gridlock on the streets of the famous musical city.
Police and fire crews were dealing with about 40 building collapses, said Metro Nashville police.
Severe storms were also whipped up by the tornadoes as they moved across the southeastern US state after midnight.
“A tornado skipped across the county,” said Nashville Mayor John Cooper on a visit to an emergency shelter.
“You do have people at the hospital and frankly there have been fatalities.”
A video posted online from east Nashville appeared to showed the tornado moving quickly across the city accompanied by lightning.
One tornado reportedly stayed on the ground into Hermitage, 20 miles (16km) east of Nashville, with buildings, bridge and roads damaged.
“Our community has been impacted significantly,” the Mount Juliet Police Department tweeted.
“We continue to search for injured. Stay home if you can.”
Country singer Carrie Underwood was one of those affected and said her husband and children had to shelter in their safe room as the tornado hit.
Hangars were destroyed at Nashville’s John C Tune Airport, with a spokesman saying it had “sustained significant damage”.
Schools, courts and rail lines were also closed – and some polling stations were damaged just hours before crucial Super Tuesday voting.
Dozens of people in the city were seen carrying their belongings through the streets after the tornado barrelled through the city.
The local Red Cross has opened a shelter for people made homeless.
Nashville Electric said 44,000 people had lost power after four substations were damaged.
Courtesy of Sky News
STORM DENNIS UPDATE: Hundreds of flights cancelled in the UK and army called in ahead of heavy winds and flooding #StormDENNIS #flights #planes #cancellations #army #SevereAlert #FloodAlert #gales #UK
Warnings are in place across the whole of the UK, while a month’s worth of rainfall is expected in places.
Hundreds of flights have been cancelled and the army has been called in as Storm Dennis prepares to hit the UK with strong winds and flooding.
The UK is bracing for disruption as the “perfect storm” approaches, bringing gusts of up to 70mph (113kmph).
The storm could bring a month’s rainfall in one day and some parts of the country could see up to 12cm (4.7in).
More than 230 easyJet flights in and out of the UK have been cancelled due to the weather on Saturday.
British Airways has said most of its flights are scheduled to go ahead as planned, but it is expecting disruption due to strong winds.
As of 9.30am on Saturday, there were 14 flood warnings – meaning people should take immediate action as flooding is expected – and 140 flood alerts, which means flooding is possible.
Forecasters have issued separate weather warnings for rain and wind covering most of the UK until Monday.
This includes amber warnings from midday on Saturday over southern Scotland, northern England, Wales and part of the South West saying that flooding could cause a danger to life.
Troops are being deployed to help with flood preparations in the Calder Valley in West Yorkshire.
The Ministry of Justice has said 75 personnel based in Catterick and 70 reservists from Yorkshire are constructing around 700m of barriers, helping to repair defences and lay down sandbags.
Calderdale Council leader Tim Swift said: “The presence of army officers in Calderdale will be a reassuring sight for the many residents and businesses who are still recovering from Storm Ciara and preparing for Storm Dennis.
“Council staff, partners, volunteers and community groups have worked tirelessly all week and will continue to work around the clock for as long as necessary to help keep people safe and to manage the flood risk.”
A Royal Navy ship is assisting in a search and rescue operation off the coast of Margate, Kent, after a man was reported overboard from a vessel at around 5:41am on Saturday.
It it is not clear if the incident is connected to Storm Dennis.
RNLI lifeboats, a police boat and the coastguard helicopter are assisting with the Navy ship with the search.
The Met Office says Storm Dennis poses a greater risk of widespread flooding than Storm Ciara the weekend before.
The Environment Agency (EA) said this is due to rain falling on already saturated ground.
Power cuts are also expected and there is a good chance train and buses will see cancellations or delays and roads closed.
Courtesy of Sky News