The National Highway Traffic Safety Administration said Monday it is opening new investigations into older Chrysler vehicles that stall after refueling without warning and Mazda cars with doors that fail to properly close.

NHTSA said it is investigating 192,076 2006 Chrysler 300C, Dodge Charger and Magnum cars quipped with 5.7L or 6.1L 8-cylinder HEMI engines. NHTSA said it has received 54 complaints of vehicles stalling while driving after refueling at a gas station — of those, 48 reported multiple problems. NHTSA said the complaints show an apparent increasing trend, with more than 50 percent received within the past eight months.

Separately, NHTSA said it is investigating 39,000 2009 Mazda6 vehicles after reviewing complaints that the door would fail to or not properly latch following attempts to close. NHTSA said in one instance, a passenger door inadvertently opened while the vehicle was in motion. Some reports said some or all three door latch mounting screws were missing.

Both automakers said they are working with NHTSA.

“We will cooperate with NHTSA and review it,” said Dan Ryan, Mazda’s director of government and public affairs.

Chrysler spokesman Eric Mayne said the company is looking at the issue.

“Chrysler Group is investigating this matter while working closely with NHTSA,” Mayne said.