But Joplin official Mark Rohr also said seven people had been rescued.

A thunderstorm carrying hail and high winds was hindering ongoing search and rescue efforts on Monday afternoon.

Mr Rohr said the tornado cut a path six miles (10km) long through the city, much of which is now without power.

Missouri governor Jay Nixon said he was "optimistic that there are still lives out there to be saved".

More than 1,150 people have been treated for injuries stemming from the tornado, the Joplin Globe newspaper reported.

The tornado knocked down power lines and telephone services remain largely cut off.

Joplin fire chief Mitch Randles said approximately one quarter or more of the city, home to about 50,000 people, had been damaged.

Roughly 2,000 buildings were damaged in the region, officials said.

Mr Nixon has declared a state of emergency and warned that more storms were on the way.

Cities in three other Midwestern states have also been badly affected. At least one person was killed in Minneapolis, Minnesota.

The White House said on Monday that President Barack Obama was being kept up-to-date on the deadly storms in the Midwest during his six-day trip in Europe.

Federal Emergency Management Agency administrator Craig Fugate is being sent to Missouri to help coordinate disaster response and recovery efforts, the White House added.

Last month, tornadoes and storms killed at least 350 people in Alabama and six other southern states.