A massive tornado that tore a 10-kilometre path across southwestern Missouri killed at least 116 people as it smashed the city of Joplin, ripping into a hospital, crushing cars and leaving behind only splintered tree trunks where entire neighbourhoods once stood.

City Manager Mark Rohr announced the new death toll at a Monday afternoon news conference. He said seven people had been rescued, and Missouri Gov. Jay Nixon said he was "optimistic that there are still lives out there to be saved."

Authorities warned that the death toll could climb as search-and-rescue workers continued their efforts. Their task was made more miserable early Monday by a new thunderstorm that brought strong winds, heavy rain and hail.

Much of the city's south side has been levelled, with churches, schools, businesses and homes reduced to ruins by winds of up to 320 km/h.

Jasper County emergency management director Keith Stammer said about 2,000 buildings had been damaged. Joplin fire Chief Mitch Randles estimated the damage covered a quarter or more of the city of about 50,000 people about 250 kilometres south of Kansas City. He said his home was among those destroyed.

An unknown number of people were injured, and officials said patients were sent to any nearby hospitals that could take them.

Police officers staffed virtually every major intersection as ambulances screamed through the streets. Rescuers involved in door-to-door searches moved gingerly around downed power lines and jagged debris, while survivors picked through the rubble of their homes, salvaging clothes, furniture, family photos and financial records, the air pungent with the smell of gas and smoking embers.

Some neighbourhoods were completely flattened and the leaves stripped from trees, giving the landscape an apocalyptic aura. In others where structures still stood, families found their belongings jumbled as if someone had picked up their homes and shaken them.

Nixon had said earlier that he feared the death toll would rise but expected survivors to be found in the rubble.

"I don't think we're done counting," Nixon told The Associated Press, adding, "I still believe that because of the size of the debris and the number of people involved that there are lives to be saved."

The National Weather Service's director, Jack Hayes, said the storm was given a preliminary label as an EF4, the second-highest rating given to twisters. The rating is assigned to storms based on the damage they cause.

Crews found bodies in vehicles the storm had flipped over, torn apart and crushed like empty cans. Triage centres and temporary shelters quickly filled to capacity. At Memorial Hall, a downtown entertainment venue, emergency workers treated critically injured patients.

At another makeshift unit at a Lowe's home-improvement store, wooden planks served as beds. Outside, ambulances and fire trucks waited for calls. In the early hours of the morning, emergency vehicles were scrambling nearly every two minutes.

View Larger Map With files from The Associated Press