Two of the dead were children, according to Mississippi Emergency Management Agency spokesman Greg Flynn.

The death toll is expected to rise as rescue crews reach hard-hit areas where structures have been badly damaged, Flynn said.

Five of the dead were from Choctaw County, in the north central part of of the state, three were from Yazoo County, north of Jackson, and one was from Holmes County, also in the north central Mississippi, he said.

Mississippi Gov. Haley Barbour, who was in Yazoo City where his home is located, called the twister “gigantic” and said that “in places (it) seemed to be to be several miles wide.”

Some residents were trapped in badly damaged homes, he said.

“They’re working to get to the people and rescue as many as they can,” said Dan Turner, a spokesman for the governor, reporting “significant injuries” in at least three counties.

In all, 12 counties were reporting injuries, with some of the injured airlifted to a level one trauma center at the University of Mississippi Medical Center in Jackson, said Jeff Rent, a MEMA spokesman.

The hospital has 10 people injured in the tornado, with four in critical condition, according to spokesman Tom Fortner.

The hospital is expecting “another one or two waves of victims” as crews are able to fully access the tornado’s path, said Richard Summers, chairman of emergency medicine at the medical center.

The hospital has crews in Yazoo City and Lexington that have been “amazed and astounded” by the amount of damage they’re seeing, Summers said.

The state’s emergency management officials have set up a command post near Highway 49 in Yazoo City and the state has activated a 25-person rapid response team from Hattiesburg that is capable of search and rescue operations.

The governor said he is activating local members of the National Guard in Yazoo City to maintain order.

President Barack Obama has “been briefed on the tragedy in Mississippi and the situation is being followed by the White House,” Obama spokesman Bill Burton said.

Barbour said that he has not yet requested emergency federal aid but that he plans to do so on Monday.

“FEMA is in contact and coordination with our state and local partners and stand ready to help if a request is made,” said Brad Carroll, a spokesman for the Federal Emergency Management Agency.

Mississippi residents reported that the path of the twister was a half-mile to a mile wide, said Mark McAllister, a forecaster with the National Weather Service in Jackson.

CNN meteorologist Jacqui Jeras said the tornado had traveled 150 miles across Mississippi, starting in the western part of the state and moving northeast before weakening as it moved into Alabama.

In Yazoo City, Fire Chief Roy Wilson said between 20 and 30 houses were destroyed, and said some people were trapped inside structures. Wilson said he didn’t yet have confirmed numbers on injuries.

“It’s in pretty bad shape so far,” he said of the city.

Speaking to reporters in Yazoo City, Barbour said 17 injured have been taken to a hospital via ambulance and that two others were airlifted to Jackson.

“By God’s grace (the tornado) did not go into the most central part of the city, the most populous, however it went through the southern edge and eastern edge of town in a number of large neighborhoods,” he said. “A number of businesses have been destroyed and others severely damaged — there are churches that have been obliterated.”

The sheriff’s department in nearby Hinds County is sending two dozen deputies and 100 inmates to assist with the response in Yazoo County and to clear debris.

In Eagle Lake, near the Louisiana border, about 30 homes were destroyed, Turner said. In Holmes County, 50 homes sustained structural damage, the National Weather Service reported.

Saturday’s tornado was part of a broad band of storms that stretched from Missouri to the panhandle of Florida, Jeras said.

The storm system struck Louisiana before it moved into Mississippi. A Tallulah, Louisiana, police dispatcher said a chemical plant in the city had been damaged, but could not give further details.

Turner said that emergency response teams had been slowed by people out surveying the effects of the storm.