The Alabama city of Tuscaloosa has been among the hardest-hit by fierce storms which have battered the southern United States.
A massive tornado - some estimates put it at a mile wide - tore through the city on Wednesday. Meteorologists say it could have been the worst in the state's history.
As the twister's approach was broadcast on local television, one presenter on WMBA told viewers: "That is something that you pray that you never, ever ever see."
The full scale of the destruction in Tuscaloosa is not yet clear, but more than 16 people are known to have been killed.
The twister "cut a path of destruction deep into the heart of the city," said Mayor Walter Maddox.
"What we faced today was massive damage on a scale we have not seen in Tuscaloosa in quite some time," Mr Maddox told reporters.
"We have hundreds of homes and businesses destroyed and hundreds more damaged."
'Roof flying off'
The city's hospital is running on emergency generators after a nearby electricity substation was knocked out by the storm.
But staff said they had still taken in more than 100 patients and were operating in full disaster mode.
"All the stuff you need to be a hospital are fine: just not necessarily all the things you need to run an office," spokesman Brad Fisher told Tuscaloosa News.
Police stations and the offices of the Emergency Management Agency (EMA) were also damaged.
Grocery manager Mike Honeysutt described cowering with his customers at the back of the shop while the storm passed overhead.
He had been monitoring its progress on the radio until he saw it through the window, bearing down on his shop.
"The power went out and the building started shaking," he told the Associated Press.
"The windows were shaking and part of the roof was flying off the building - the windows came into the front and then the wind started blowing stuff off of the shelves.
Will Nevin told local newspaper the Birmingham News: "My wife and I were watching the weather coverage until the monster was right up on us."
"Then it was the mad dash to the bathroom where the lights flickered, pulsed and finally gave up.
"Even on the ground floor of our two-storey apartment building, we could hear the wildness above us."
Student James DiNiro told the BBC the damage in the city was comparable to "photos from cities in World War II."
"Me and a few of my friends helped pull a woman with a very severe head wound out of the rubble of her house and get her to the hospital," he said.
"Her situation, like many others, appears grave."
There was relief when a child was found alive beneath one pile of debris and was carried away by firefighters.
But officials have warned that with more storms forecast in the coming days, the danger is not yet over for the town.