Tornadoes kill five more in Oklahoma.

OKLAHOMA CITY, United States, 1 June (Reuters) - Tornadoes killed five people in central Oklahoma, including a mother and her baby, threatening Oklahoma City and the hard-hit suburb of Moore, before moving northeast into the early hours of Saturday.

The National Weather Service said the threat of severe weather will shift toward the neighboring states of Illinois and Missouri, where Governor Jay Nixon declared a state of emergency on Friday.

The tornadoes struck the region just 11 days after an EF5 category tornado, the most powerful in the classification of these natural phenomena, devastated Moore and killed 24 people.

The mother and baby died Friday while traveling on Interstate 40, west of Oklahoma City, when their vehicle was caught in a storm and they were sucked out, said Oklahoma Highway Patrol spokeswoman Betsy Randolph.

The highway was closed due to the storm, resulting in several accidents and injuries.

Two of the five deaths in Oklahoma on Friday occurred in Union City and one in El Reno, in rural areas west of Oklahoma City, said Medical Examiner's Office spokeswoman Amy Elliott. She could not confirm where the other deaths occurred.

More than 40 people were being treated for storm-related injuries, including five in serious condition, among them a child, according to an Oklahoma hospital.

Meteorologists had already declared a tornado emergency for the Oklahoma City metropolitan area and even issued a tornado warning for Moore, which has suffered limited damage since the recent storms, said a police officer sent to the city.

A tornado struck Interstate 40 toward Oklahoma City, overturning trucks and hurling hay bales, a witness said. TV footage showed downed power lines and tossed cars as the weather system dumped at least 3 centimeters of rain, stranding motorists in the flood.

"For reasons that are unclear to me, more people went out into the streets than we expected. Everyone reacted differently to this storm, and as a result, an extremely dangerous situation was created," said Oklahoma City Mayor Mick Cornett.

"I think we're still a little shaken by what happened in Moore. We're still burying children and victims, so our emotions are still running high," he added.

Brandi Vanalphen, 30, was among hundreds of drivers stuck in traffic as she tried to escape the tornado system in the suburb of Norman.

"What scared me was getting stuck in traffic," she said. "I started seeing flashes of energy to the north... people started driving on the grass."

Oklahoma Governor Mary Fallin told CNN that drivers faced great danger if they were stranded on any highway in the tornado's path.

"What we saw from the tornadoes that passed through Moore and others last week was that people who were in cars on the Interstate were killed," Fallin told CNN.

(By Heide Brandes, with additional reporting by Suzi Parker in Little Rock; Brendan O'Brien in Milwaukee; Tom Brown in Miami; Colleen Jenkins in Winston-Salem; Tim Bross in St. Louis; and Karen Pierog in Chicago)