Updated 5 p.m.

Violent thunderstorms produced tornadoes in central Oklahoma that killed nine  people including a mother and her baby and menaced Oklahoma City and its hard-hit suburb of Moore, authorities said.

The mother and baby were killed while travelling on Interstate 40, just west of Oklahoma City, when their vehicle was picked up by the storm, said Betsy Randolph, spokeswoman for the Oklahoma Highway Patrol.

The interstate was shut down due to the storm, with multiple crashes and injuries. Two of the deaths occurred in Union City and one was in El Reno, west of Oklahoma City, said Amy Elliott, a spokeswoman for the state Office of the Chief Medical Examiner.

She could not immediately confirm where the other deaths occurred. Some 40 to 50 people were being treated for storm-related injuries, including five patients in critical condition, among them a child, according to the Integris Health hospital system. National Weather Service meteorologists had earlier declared a tornado emergency for parts of the Oklahoma City metropolitan area, and a twister touched down in Moore, which was hit by a massive EF-5 twister last week that killed 24 people.

A tornado also rampaged down Interstate 40 toward Oklahoma City, tipping over dozens of trucks, one witnesses said.Television images showed downed power lines and tossed cars as the storm systems dumped heavy rains, stranding motorists in flood water.

"For reasons that are not clear to me, more people took to the roads, more than we expected. Everyone acted differently in this storm, and as a result, it created an extremely dangerous situation," Oklahoma City Mayor Mick Cornett said. "I think we are still a little shaken by what happened in Moore. We are still burying children and victims, so our emotions are still strong," he added.