In the US state of Kentucky at least 50 people are believed to have been killed by a tornado.

"I fear that there are more than 50 deaths in Kentucky, probably closer to 70 to 100," said Governor Andy Beshear to journalists on Saturday.

Severe storms with a whole series of tornadoes hit several states on Friday - in Illinois, the fate of around a hundred employees in an Amazon warehouse, which was partially destroyed, was initially unclear.

The storms devastated several counties in Kentucky.

According to Governor Beshear, the strongest tornado brought winds of about 322 kilometers per hour with it.

It was the worst tornadoes in Kentucky's history.

In the city of Mayfair, the roof of a candle factory collapsed, resulting in numerous victims.

"I declared a state of emergency before midnight," said the governor.

One of the "darkest days" in Kentucky history

Beshear sought assistance from President Joe Biden.

"Kentucky needs federal aid to respond to this event," said a letter to Biden published by the governor on Saturday.

Power outages are widespread.

17 of the 120 counties in the state were affected by the disaster.

Beshear also activated the National Guard to support affected communities.

Kentucky Civil Protection Director Michael Dossett told CNN that tornadoes had carved a 200-mile (320 kilometers) swath from southwest to northeast in the southeastern state.

He spoke of one of the "darkest days" of Kentucky.

Other states were also hit by the devastating storm system on Saturday night.

CNN reported dozens of tornadoes in six states.

Other states in the southeast and in the center of the country were also hit: The rescue workers were concerned about the fate of around one hundred employees of an Amazon warehouse in the state of Illinois, who were trapped in the building that was partially destroyed by a tornado.

They were on the night shift that processed Christmas orders.

At the time of the accident, a tornado warning was in effect.

Pictures on US news channels and online networks showed that a large part of the roof of the warehouse in Edwardsville had been torn off and a wall had fallen into the building.

Debris could be seen everywhere.

The local civil protection agency spoke of numerous victims.

At first it was unclear whether there were dead or injured.

Illinois Governor JB Pritzer said he was praying for the people of Edwardsville.

Amazon spokesman Richard Rocha said the group is reviewing the situation.

"The safety and wellbeing of our employees and partners is now our top priority." 

At least one person was killed in a nursing home in Arkansas and 20 more were initially trapped in the facility, according to local media reports.

Officials later reported that the rescue workers had been able to free those trapped from the building, which had been "largely destroyed".

At least two people died in Tennessee, a civil protection representative told local media.