Tornadoes ripped through Tennessee early Tuesday, leaving at least 25 people dead, destroying buildings and toppling power lines hours before the southern US state voted in Super Tuesday primaries.

Voting hours were extended due to the devastation the twisters wrought when they touched down shortly after midnight -- rubble was strewn across the state capital Nashville.

Residents ran for their lives as their homes came down around them. Tens of thousands lost power to their homes, officials said.

"TAKE COVER NOW! THIS IS AN EXTREMELY DANGEROUS STORM!!!" the National Weather Service tweeted as one tornado tore through an area west of Nashville.

Television broadcast showed cars piled up, hangars destroyed and what appeared to be dozens of aircraft smashed into each other at Nashville's John C. Tune Airport.

The Nashville Police Department circulated aerial photographs of many buildings missing roofs and homes destroyed -- standing next to houses that escaped damage.

"In the hours ahead, we will continue deploying search and rescue teams, opening shelters across the state, and sending emergency personnel to our communities hit hardest," Governor Bill Lee wrote on Twitter.

Lee said late Tuesday that the toll had risen to 25 during the day.

Among the victims were two people in Nashville killed after being struck by debris, police said.

Mayor John Cooper said around 150 people had been transported to medical facilities while nearly 50 buildings had collapsed in the city, the hub of the US country music scene.

US President Donald Trump said that he would visit the stricken areas Friday.

"We send our love and our prayers of the nation to every family that was affected, and we will get there and we will recover and we will rebuild and we will help them," Trump said.

The series of severe storms that passed through Tennessee caused major damage to buildings, roads, bridges, utilities and businesses, the Tennessee Emergency Management Agency (TEMA) said.

"Tornado damage has been reported throughout West and Middle Tennessee including downtown Nashville," it added.

Overturned tractor trailers and other vehicles littered interstate highways.

'The house just exploded

In the city's East Nashville neighborhood, resident David Haskell said that he and his wife bolted into their storm shelter after an alarm on their phone went off.

"Ten seconds later. the house just exploded," he told the local Tennessean newspaper, standing in front of his home, with its crumbled walls and destroyed roof.

Cooper wrote on Twitter that "Nashville is hurting, and our community has been devastated," as he urged people to lend a helping hand.

More than 73,000 customers were without power amid scattered storms throughout the day, TEMA reported.

Tennessee is one of 14 states voting in the crucial Super Tuesday primaries, which will help determine the Democratic Party nominee for November's presidential election.

Cooper told a news conference that 15 polling stations had been affected by storm damage, less than 10 percent of the total.

Some polling stations would stay open until 10:00 pm Central time (0400 GMT Wednesday), a local judge ruled, to allow those affected by the tornado to vote.

The Democratic candidates vying to take on Trump in November's election were quick to acknowledge the disaster.

"We have been watching the news coming out of Tennessee with heavy hearts," former New York mayor Mike Bloomberg tweeted.

Massachusetts Senator Elizabeth Warren said she was "heartsick for the victims."

Country music star Dolly Parton led expressions of support on Twitter, along with singer Taylor Swift.

Actress Reese Witherspoon, who grew up in Nashville, tweeted that she was "saying special prayers for the families who lost loved ones."

The storms hit exactly a year after tornadoes cut across Alabama, which lies directly south of Tennessee, killing 23.