AFP, Washington

At least 50 people are dead after a tornado ripped through the southeastern US state of Kentucky, its governor told reporters, as storms ravaged large swathes of the country.

Several counties in Kentucky were devastated, with the strongest tornado tearing 200 miles through the state, governor Andy Beshear said.

“I fear that there are more than 50 dead ... probably closer to somewhere between 70 and 100, it’s devastating,” he said, adding this was the “most severe tornado event in Kentucky’s history”.

The governor said a roof collapse at a candle factory “resulted in mass casualties” in the city of Mayfield.

“Before midnight I declared a state of emergency,” Beshear said.

The tornado came as storms wreaked havoc in multiple US states.

A storm earlier tore through a massive Amazon warehouse in the US state of Illinois on Friday, officials said, with local media reporting around 100 workers trapped inside.

Officials were working through the early hours of Saturday to rescue employees at the facility -- a third of which was reduced to rubble -- who were on the night shift processing orders ahead of the Christmas holidays.

The Collinsville Emergency Management Agency described it as a “mass casualty incident” with “multiple subjects trapped at Amazon Warehouse”.

A tornado warning had been in effect in the area at the time of the incident.

In Arkansas, one person was killed and 20 others were trapped after a tornado struck the Monette Manor nursing home, US media reported. In Tennessee, at least two people were killed in storm-related incidents, an emergency management official told local media.