More than 100 people are feared dead after powerful tornadoes caused catastrophic damage in a number of US states.
Kentucky was the worst impacted state, with the state's governor saying dozens of people had died.
Homes and businesses were also destroyed, with authorities saying they still weren't sure of the full extent of the damage.
Arkansas, Illinois, Missouri and Tennessee were also hit by the 'deadly and devastating' tornadoes.
Speaking on Saturday, US President Joe Biden said it's likely to be "one of the largest tornado outbreaks in our history".
This morning, I was briefed on the devastating tornadoes across the central U.S. To lose a loved one in a storm like this is an unimaginable tragedy. We’re working with Governors to ensure they have what they need as the search for survivors and damage assessments continue.
— President Biden (@POTUS) December 11, 2021
He said: "Jill and I pray for those who have lost loved ones and for those who are uncertain of the fate of their loved ones.
"They lost their homes. They lost their businesses. And it’s a tragedy. It’s a tragedy. And we still don’t know how many lives were lost or the full extent of the damage.
"But I want to emphasise what I told all the governors: The federal government will do everything — everything it can possibly do to help."
Kentucky Governor Andy Beshear said it was "the worst, most devastating and most deadly tornado event" in the state's history.
He said at least 70 lives had been lost, but that was likely to rise to more than 100 people.
He said 110 people were working in one factory when the storm hit, but just 40 people had been rescued so far - saying it would be a "miracle" if anyone else was found alive.
Parts of some towns had "no homes left standing" after the storm tore through the area.
In Illinois, the walls of an Amazon warehouse collapsed during the storm, leaving six workers dead.
Around 45 other workers made it out of the collapsed building safely.
It was unclear how many others remained missing, but local authorities said they'd given up hope of finding any more survivors in the rubble.