The U.S. government issued an urgent plea to more than 4.7 million people to get the air bags in their cars fixed, amid concern that a defect in the devices can possibly kill or injure the driver or passengers.

The inflator mechanisms in the air bags can rupture, causing metal fragments to fly out when the bags are deployed in crashes. Safety advocates say at least four people have died from the problem and there have been multiple injuries.

Multiple automakers have recalled vehicles in the U.S. over the past two years to repair air bag inflators made by Takata Corp., a Tokyo-based supplier of seat belts, air bags, steering wheels and other auto parts. In a statement Monday, the National Highway Traffic and Safety Administration warned owners of those cars to act right away.

The agency has been investigating the problem since June, and has cited reports of six inflators rupturing, causing three injuries.

Worldwide, automakers have recalled about 12 million vehicles because of the problem.

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The warning covers cars made by Toyota, Honda, Mazda, BMW, Nissan, General Motors and Ford. Passenger or driver air bags or both could have the faulty inflators. Safety advocates say the problem could affect more than 20 million vehicles in the U.S.

The rare action by federal regulators comes three weeks after a Sept. 29 crash near Orlando, Florida, that claimed the life of a 46-year-old woman. In that crash, Hien Thi Tran suffered severe neck wounds that could have been caused by metal fragments flying out of the air bag on her 2001 Honda Accord. Her Accord was among the models being recalled.

One police agency concluded that the air bags caused her wounds, while another is still investigating. NHTSA is seeking information in the case.

Toyota on Monday issued a recall covering passenger air bags in 247,000 older model vehicles including the Lexus SC, Corolla, Matrix, Sequoia and Tundra. Like many earlier recalls, Toyota's covers vehicles in South Florida, along the Gulf Coast, in Puerto Rico, Hawaii, the U.S. Virgin Islands, Guam, Saipan and American Samoa — all areas that have high absolute humidity.

Toyota said it's working with Takata to pinpoint the cause of the rupture and to gauge the influence of high absolute humidity, which is a measurement of water vapor in the air.

Toyota could expand the recall to more areas pending further testing, according to spokesman John Hanson. Toyota says it knows of no crashes or injuries in the recalled cars.

NHTSA urged people to check if their car has been recalled by going to https://vinrcl.safercar.gov/vin/ and typing in their vehicle identification number.

Clarence Ditlow, executive director of the nonprofit Center for Auto Safety, estimated there are 20 million to 25 million cars in the U.S. alone that are equipped with the faulty air bags.

In the Florida case, Tran turned left in front of another vehicle and the front ends collided. Her air bag inflated. The original report on the death said the seat belt could not have cut the right side of her neck. Also, there was no broken glass and no other apparent cause of the neck wounds.

Initially the case was turned over to the Orange County Sheriff's Office, whose homicide investigators determined that the air bag caused Tran's neck injuries, the Orlando Sentinel reported. Because the death appears to be traffic-related, the matter was sent back to the Florida Highway Patrol, which has not finished its investigation.

The Highway Patrol will call in an air bag expert to help make the determination, said Sgt. Kim Montes. The car's steering wheel and spokes were not damaged and appeared to be a normal air bag deployment, she said. Investigators also will look for evidence of metal fragments in the car and try to determine what caused Tran's neck wounds, Montes said.

Last week, two U.S. senators questioned why the safety agency is limiting the recall to certain regions.

They cited the May 27, 2009, death of 18-year-old Ashley Parham of Oklahoma City as proof the problem can occur in areas where humidity isn't so prevalent. Parham was driving a 2001 Honda Accord across a high school parking lot in Midwest City, Oklahoma, when it hit another car. The air bag inflated and sent shards of metal into her neck, causing her death.

Takata said Monday it supports Toyota's recall decision and will continue to support NHTSA and its customers with replacement parts and technical analysis.