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A man carries a young girl who was rescued after being trapped with her mother in their home after a tornado hit Joplin in Missouri on Sunday evening. Image Credit: AP

Joplin, Missouri: A massive tornado that tore nearly a one-km wide 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 neighborhoods once stood.

In pictures: Tornado ravages Missouri

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

US weather officials said the tornado that hit at dinner time on Sunday may have been the single deadliest in the country since 1953.

Rescue crews from throughout the region worked all night and into Monday morning in the town of about 50,000 people, searching for anyone still alive in the rubble.

An unknown number of people were injured and officials said they expected to find more bodies as they dig through collapsed homes and businesses.

The tornado blew the roof off St John's hospital where about 180 patients cowered, and some 2,000 homes and other buildings were destroyed. It flattened whole neighbourhoods, splintered trees, flipped cars and trucks upside down and into each other.

A number of bodies were found along the city's "restaurant row," and a local nursing home took a direct hit, Newton County Coroner Mark Bridges said.

"It is a significant tragedy," said Missouri Governor Jay Nixon. "We're working on all cylinders. We've got to get an active and complete search ... to make sure if there is anyone still alive in the rubble that we get them out."

The city's residents were given about 20 minutes notice when 25 warning sirens sounded throughout the southwest Missouri town around 6pm CDT, said Jasper County Emergency Management Director Keith Stammers.

But the governor said many people likely were unable to get to shelter in time. "The bottom line was the storm was so loud you probably couldn't hear the sirens going off." He declared a state of emergency and called out the Missouri National Guard to help.

Make-shift morgue

"The loss of life is incredible," said Joplin Mayor Mike Woolston. "We're still trying to find people. The outlook is pretty bleak."

Two refrigerated trucks were brought in to serve as a make-shift morgue at a local university and more were being brought in to handle the additional bodies expected, the coroner said.

Joplin City Councilwoman Melodee Colbert-Kean, who serves as vice mayor, said the town was in a state of "chaos."

"It is just utter devastation anywhere you look to the south and the east — businesses, apartment complexes, houses, cars, trees, schools, you name it, it is levelled, levelled," she said.

President Barack Obama called the governor on Sunday evening to "extend his condolences" to the families of Joplin. White House spokesman Nicholas Shapiro said Federal Emergency Management Agency head Craig Fugate was on his way to Joplin to help with recovery.

The tornado in Joplin was the latest in a string of powerful twisters that has wreaked death and devastation in recent weeks.

Severe damage

Tornados killed more than 300 people and did more than $2 billion (Dh7.34 billion) in damages to the US south last month, killing more than 200 in Alabama alone.

On Saturday night, a tornado ripped through Reading, Kansas, killing one and damaging 200 homes and businesses. Another person was killed in a tornado in Minneapolis on Sunday.

The path of the tornado through Joplin was estimated at 9.5 km long and about one km wide.

Sharon Hurtt 60, and Bill Dearing, 59, had no basement to flee to when the tornado descended on their single-storey home, so they huddled in a closet between two bedrooms. Within minutes, the roof was gone and powerful winds ripped the door off the closet.

"We were holding on to keep from blowing away," said Hurtt.

A mattress blown off the bed somehow became wedged in the doorway.

"It probably saved us," said Hurtt.