US President Joe Biden has said the government will do everything it possibly can to help central areas of the country devastated by tornadoes.
Emergency workers search what is left of the Mayfield Consumer Products Candle Factory where it is feared dozens have died. Photo: AFP
Biden has signed a Federal Emergency Disaster Declaration, releasing funds for Kentucky, the worst affected state.
He said the storms were among the largest in US history.
More than 70 people died in Kentucky in Friday night's storms, including dozens in a candle factory, and the death toll is expected to rise above 100.
Emergency teams are searching through the rubble of the factory, in the town of Mayfield, which was hit directly.
More than 40 people have been rescued out of some 110 in the factory but Kentucky Governor Andy Beshear said it would be a miracle if anyone else was found alive.
The conditions facing the authorities are hugely challenging, with the police station in Mayfield destroyed and firefighters' equipment damaged.
Tens of thousands of people in the state are also without power and water.
At least 12 people died as tornadoes wreaked havoc in other states, including six in an Amazon warehouse in Illinois.
Biden said he was praying for those who had lost, or who were uncertain about, their loved ones.
"The federal government will do everything it can possibly do to help," he said. "We're going to get through this together."
The president said teams from the emergency agency Fema would go to Kentucky on Sunday to offer additional resources including help with temporary housing for those whose homes had been destroyed or badly damaged.
Governor Andy Beshear has declared a state of emergency in Kentucky. He said Mayfield and everywhere along the 227-mile (365-km) path of the tornado - almost all in Kentucky - were devastated.
"It's indescribable, unlike anything I've ever seen," he said.
"You see parts of industrial buildings, roofs, or sightings in trees, if trees are lucky enough to stand.
"Huge metal poles bent in half if not broken, buildings that are no longer there, huge trucks that have been picked up and thrown. And sadly far too many homes that people were likely in, entirely devastated."
"There are a lot of families that need your prayers," he added.
'Dire situation'
Deaths had been reported in several counties, but the loss of life in the Mayfield factory could exceed that of any tornado event in a single location in state history, the governor added. More than 100 people were inside when it hit.
Beshear said 40 people had been rescued at the factory and he was praying for more survivors, but it was a "very dire situation".
Local officials who visited the scene spoke of heavy machinery displaced by the storm, as well as drums leaking corrosive liquid.
Martin Bolton (left) and shop owner Danny Wagner try to shut off a leaking gas meter after his Mayfield automobile repair shop was destroyed by the tornado. Photo: AFP
US President Joe Biden tweeted that he had been briefed about the tornadoes on Saturday morning.
"To lose a loved one in a storm like this is an unimaginable tragedy," he said. "We're working with Governors to ensure they have what they need as the search for survivors and damage assessments continue."
Police said the tornado caused "significant damage" across the western parts of the state. A train was derailed during extreme winds in Hopkins County, Sheriff Matt Sanderson told WKYT-TV.
He also described how two children were reported missing during a tornado but were then found in a bathtub that had been pulled outside by the force of the wind.
"There were two children in the Barnsley area that were missing and they were actually found in a bathtub not where the house was originally standing," he said.
The Amazon warehouse in Edwardsville in southern Illinois was damaged during a tornado on Friday night, the authorities said.
It is not yet clear how many people were hurt by the roof collapse, but local emergency services have called it a "mass casualty incident" on Facebook.
Illinois police chief Mike Fillback said at least one person had died.
Sarah Bierman said her partner was still missing.
"I talked to him about 8 o'clock tonight, a little before I texted him, and he was returning to the warehouse to drop his van off. And I haven't heard from him since," she told the Reuters news agency.
"I decided to come down here to see what was going on. I had no idea the building looked that bad. And I'm just ... I'm worried sick. I just want to know if he's okay," she added.
"My prayers are with the people of Edwardsville tonight, and I've reached out to the mayor to provide any needed state resources," Illinois Governor JB Pritzker tweeted.
Later reports said 30 people had been rescued and two were airlifted to hospital in St Louis, in neighbouring Missouri. Rescue teams are still sorting through the rubble.
Tennessee state Emergency Management Agency spokesman Dean Flener said three people had been killed in the northwest of the state. No further details were given.
In north-eastern Arkansas, one person died, five were seriously injured and 20 people were trapped inside in a nursing home after it partly collapsed, local official Marvin Day said.
The trapped people were rescued but the building was "pretty much destroyed", he added.
- BBC