At least two reported dead as tornadoes hit US

Elsewhere in Illinois, several flights in and out of Chicago O'Hare International Airport have been cancelled due to the weather.

People on social media say they have been urged to take cover in the tunnels of the airport.

An hour ago, the airport tweeted: "Severe weather is imminent at O'Hare International Airport.

"If you're in the airport, please exercise caution, and follow the instructions of all airport personnel.

"Service on the Airport Transit System is suspended until the threat of severe weather has passed."

SnapMapCopyright: SnapMap

The BBC's US partner CBS has reported the collapse of a theatre roof in Illinois, as high winds blew through the area.

Videos on social media appear to show debris inside and outside the Apollo Theater in Belvidere, with many emergency vehicles outside.

It's not clear if there are any injuries or deaths yet. Stay with us while we bring you the latest.

An eyewitness has captured two tornadoes from the roadside in Keota, Iowa.

Pulaski County Sheriff’s OfficeCopyright: Pulaski County Sheriff’s Office

More images on social media show major damage left in parts of Arkansas.

Along with a photo of an overturned lorry on an Arkansas highway, Pulaski County Sheriff’s Office tweeted:

"First responders are on scene in the Rodney Parham and Jacksonville areas (as seen in the picture).

"Do not stop to survey damage. If you are traveling home you may have to take an alternate route."

Make sure to gather emergency supplies beforehand if possible and sign up for tornado warnings if your area.

Where should you seek shelter from a tornado?

• Go inside, but avoid high floors and windows which can easily break. Move to a basement if available - if not, seek an interior room
• Get low and cover your head and abdomen area
• Taking cover with thick padding like a mattress or blankets can also help shelter you
• Do not stay in a mobile home during a tornado

National Weather ServiceCopyright: National Weather Service

"We believe it's just one [tornado] that occurred from one continuous thunderstorm," Little Rock National Weather Service forecaster Jim Reynolds has told the BBC.

"The tornado that we've seen started in west Little Rock and then continued east northeast and as kind pulled back up into the sky for a little bit and then came back down."

He says its too early to say how far it tracked across the ground.

Andrew CollinsCopyright: Andrew Collins

Earlier Arkansas State Representative Andrew Collins tweeted this image of his area in Little Rock which he says "took a hit" from the tornado.

Emergency vehicles are at the scene as many residents look on at the debris strewn and scattered on the road.

The Weather ChannelCopyright: The Weather Channel

• Tornado sirens have been sounding off in Davenport, Iowa as someone captures a funnel forming overhead
• The Weather Channel said the central Tennessee, northern Mississippi and northwestern Alabama could see particularly dangerous storms with several strong tornadoes, destructive winds and large hail
• Ping-pong size hail has been reported in northern Illinois

In the last few moments the mayor of Little Rock - Arkansas's biggest city - has said there are no confirmed deaths.

Writing on Twitter Frank Scott, Jr. said: "At this time, we know of 24 people who have been hospitalised at Little Rock hospitals and we are not aware of any fatalities in Little Rock at this time.

"Property damage is extensive and we are still responding."

Meanwhile, Arkansas Children’s Hospital says it has treated children who were injured, according to an email from spokeswoman Hilary DeMillo in the Arkansas Democrat-Gazette.

Some more updates to bring you from Governor Sarah Huckabee Sanders who says there is "widespread damage" in the Arkansas city of Wynne.

Wynne, a town of some 8,000 people, is around 170km (105 miles) north-east of Little Rock, which was hit by a tornado earlier today.

Governor Sanders wrote on Twitter: "I’ve been in touch with local officials for updates and to direct state resources. Please follow the direction of local authorities.

"Praying for the safety of all Arkansans who are in the path of these storms."

The National Weather Service has 28 million people under tornado watch, calling the situation "very serious".

The watch is effective until 10pm local time for portions of northeast Illinois, northwest Indiana, southern Wisconsin and Lake Michigan.

There are threats of severe tornadoes and wind gusts to 70 mph (112 km/h) as well as large hail - 1.5in (3.8cm) in diameter.

NWSCopyright: NWS

We are starting to get more images of the damage left in the wake of the "catastrophic" twister that touched down in the the southern US state of Arkansas.

This video shows downed trees and damaged buildings.

Let's bring you an update on casualty numbers as we continue to get more and more updates from officials.

A spokesperson for the Baptist Health Medical Centers in Little Rock and North Little Rock says the two hospitals are treating 21 people for injuries.

According to CNN and Accuweather five of those patients are in critical condition.

We are still at the early stages of working out the extent of the damage in Little Rock and across Arkansas following the tornado outbreak but here is what we know so far:

• University of Arkansas for Medical Sciences Medical Center says it is expecting more than a dozen patients
• Hospital spokeswoman Leslie Taylor said it is operating at a mass casualty level - although updated numbers are yet to be confirmed
• Governor Sarah Huckabee Sanders says "significant damage" has occurred in central Arkansas
• Images on social media appears to show a Little Rock fire station sustaining damage to its roof with debris scattered around the building
• According to United States Power Outage map - over 93,000 homes are without power in Arkansas
• Elsewhere in Little Rock, cars have been overturned and various buildings in the city have been destroyed
• The mayor of Little Rock says a temporary emergency shelter has been set up at at Hall High School
• Several road closures remain in place across the city

Some more updates from Arkansas Governor Sarah Huckabee Sanders who confirms she has activated the state's national guard, a US state-based military force that is often called to respond to emergencies such as natural disasters

"They will be assisting Arkansas State Police and local law enforcement around the state," she writes on Twitter.

Missouri has become the second area today to declare a state of emergency as plenty of weather warnings remain in place across the United States.

Governor Mike Parson activated the state emergency operations plan moments ago - as well as the Missouri National Guard.

This is all as a result of severe weather heading towards the state.

Writing on Twitter he says: "Parts of Missouri are already experiencing severe weather with more forecasted across the state throughout the evening.

"While we pray for Missourians' safety and that extensive response efforts will not be needed, state government must always be prepared.

"We stand ready to assist and urge all Missourians to heed weather warnings and to take precautions to protect themselves and their loved ones."

The executive order will expire on 30 April, unless terminated or extended, according to the governor's office.

We know several states are under tornado warnings amid other severe weather alerts across the United States.

Earlier, Bill Bunting, the operations chief for the Storm Prediction Center, told the BBC the last time there were separate such high-risk warnings simultaneously was more than ten years ago in April 2012.

Speaking after the tornado in Little Rock he said: "At the moment, things are unfortunately playing out just as we have feared.

"I think the next couple of hours are unfortunately going to be very active with severe thunderstorms, tornadoes and intense damaging straight-line winds.

"We believe the tornadoes will be on par with what we saw last week. The question is, will they track? And what structures will be in their path? And that will largely determine the impact."

A tornado that has destroyed buildings and overturned cars has been caught on camera from Baptist Health hospital in Little Rock, in the US state of Arkansas.

Videos have been circulating on social media, showing it moving across the city.