The Oklahoma medical examiner's office says at least 51 people, including children, have been killed in the tornado that hit Oklahoma City's suburbs. The death toll is expected to rise as rescue workers make their way through the debris.

Neighborhoods have been flattened and fires were sparked after an EF-4 tornado with winds up to 320 km/h ripped through Moore, a community of about 41,000 residents south of Oklahoma City late Monday afternoon.

The U.S. National Weather Service issued an initial finding that the tornado was an EF-4 on the enhanced Fujita scale. That would rank it as the second most-powerful type of twister.

The tornado was estimated to measure nearly a kilometre wide.

Developments:

  • Tornado warnings were in effect for parts of Texas, Oklahoma, Arkansas, Kansas, Missouri, Iowa and Illinois.
  • At least 120 people were reported hurt, including about 70 children.
  • U.S. President Barack Obama spoke to Oklahoma Gov. Mary Fallin and assured her FEMA would deploy an assistance team to the state.
  • 80 National Guard members have been deployed to assist with search-and-rescue operations.
  • Phone lines to stricken areas were down and cellphone networks are congested.

Video footage on Monday shows streets and lawns in Moore, Okla., littered with wood, insulation and twisted metal from obliterated buildings and cars.

Fallin told reporters Monday evening that “our prayers and our thoughts are with the Oklahoma families that have been hit hard by this terrible storm these last two days, and in particular our hearts are just broken for the parents who are wondering the state of their children who are in the schools that have been hit today.”

Fallin said “we are doing everything we can as a state” to get the necessary emergency personnel on the ground “to make sure we have looked under every single piece of debris and other every building” to find the lost and injured.

She said she has had offers of help from several states in addition to the federal aid that has been promised.

Plaza Towers Elementary School in the suburb was directly hit by the tornado on Monday afternoon. Rescuers could be seen pulling some children out of the rubble hours after the tornado struck. A triage centre was set-up in the parking lot to treat survivors.

The school suffered extensive damage and the walls had fallen in or had collapsed.

James Rushing lives across the street from the school, where his five-year-old son Aiden is a student. Rushing ran to the school when he heard reports of a tornado approaching.

“About two minutes after I got there, the school started coming apart,” Rushing said.

Rescue workers fanned out across the area, pulling residents from piles of debris where their homes once stood. Rescue efforts were to continue through the night.

The same suburb was hit hard by a storm with the highest winds ever recorded near the earth’s surface in 1999.

Dozens of other tornadoes ripped through the U.S. this weekend, causing extensive damage in several cities and killing two elderly men.

Storms were reported in Iowa, Kansas and Oklahoma but most of the damage was concentrated in Kansas and Oklahoma.

A mobile home park in Shawnee, Okla. seemed to take a “dead hit” from the storm, according to one resident.

James Hoke emerged from a storm cellar, where he was holed up with his wife and two children, only to discover their mobile home had vanished.

“It took a dead hit,” he told the Associated Press. “Everything is gone.”

Last Wednesday night, a tornado struck the town of Granbury, Texas, killing six people.