MOORE, Okla. -- A tornado of rare power roared through an Oklahoma City suburb, killing at least 51, flattening neighbourhoods with winds up to 200 mph (320 kilometres) and destroying at least one school. Officials said children were among the dead.
The death toll was expected to rise, an Oklahoma Medical Examiner's Office spokeswoman said. Rescuers swarmed the debris as darkness fell and rain began to fall. More than 140 people were being treated at hospitals, including about 70 children. Some were in critical condition.
"Hearts are broken" for parents looking for their children, Governor Mary Fallin told a news conference.
The ferocious storm -- less than 1 per cent of all tornadoes reach such wind speed -- ripped through the suburb of Moore in a Midwest region of the U.S. known as Tornado Alley. Block after block lay in ruins. Cars and trucks were left crumpled.
The National Weather Service estimated that the tornado reached up to a half-mile (.8 kilometres) wide and was an EF-4 on the enhanced five-point Fujita scale, the second most powerful type of twister.
In video footage, the dark funnel cloud moved slowly across the landscape for more than half an hour, scattering shards of wood, pieces of insulation, shingles and glass over the streets.
The focus quickly turned to Plaza Towers Elementary School, where the storm tore off the roof, knocked down walls and turned the playground into a mass of twisted plastic and metal.
Several children were pulled alive from the rubble. Rescue workers passed them down a human chain to a triage centre in the parking lot.
James Rushing, who lives across the street, heard reports of the approaching tornado and ran to the school, where his 5-year-old foster son, Aiden, attends classes. Rushing believed he would be safer there.
"About two minutes after I got there, the school started coming apart," he said.
The students were put in the restroom.
After the tornado passed, Tiffany Thronesberry said she got a panicked call from her mother, Barbara Jarrell.
"I got a phone call from her screaming, 'Help, help! I can't breathe. My house is on top of me!"' Thronesberry said. She hurried to her mother's house, where first responders had already pulled her out with cuts and bruises.
Dangers remained. Downed power lines and open gas lines posed a risk Monday night, Police Capt. Dexter Nelson said. Television footage showed at least one fire in the debris.
The same suburb was hit hard by a tornado in 1999. That storm produced the highest winds ever recorded near the Earth's surface -- 302 mph (486 kph).
"Oklahoma City has had more tornado strikes than any other city in the United States," the city government's website says.
President Barack Obama called Fallin to express his concern.
