Tornadoes devastate Tennessee, killing at least 22 people

Tornadoes ripped across Tennessee as people slept early on Tuesday, shredding at least 140 buildings and killing at least 22 people.

Authorities described painstaking efforts to find survivors in piles of rubble and wrecked basements as the death toll climbed.

One twister caused severe damage across a 10-mile (16 km) stretch of downtown Nashville, wrecking businesses and homes and destroying the tower and stained glass of a historic church. Another erased homes from their foundations along a two-mile (3.2 km) path in Putnam County.

Daybreak revealed a landscape littered with blown-down walls and roofs, snapped power lines and huge broken trees, leaving city streets in gridlock.

Schools, courts, transit lines, an airport and the state Capitol were closed.

More than a dozen polling stations were damaged, forcing Super Tuesday voters to wait in long lines at alternative sites.

The death toll jumped to 22 on Tuesday as first responders gingerly pulled apart the wreckage, hoping to find people alive in the rubble of their homes.

Putnam Sheriff Eddie Farris said only 30 per cent of the disaster area had a "hard check" by mid-day.

"A lot of these homes had basements and we're hopeful there are still people down in there," he said.

Nashville residents walked around in dismay as emergency crews closed off roads. Roofs had been torn off apartment buildings, large trees uprooted and debris littered many sidewalks. Walls were peeled away, exposing living rooms and kitchens in damaged homes. Mangled power lines and broken trees came to rest on cars, streets and piles of rubble.

President Donald Trump announced plans to visit the disaster area on Friday.

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