The safety recall in parts of the United States of millions of vehicles with potentially defective air bags made by Japan's Takata Corp (7312.T) may expand to include General Motors Co (GM.N), according to documents filed this week with U.S. regulators.

More than 4.3 million cars produced by automakers including Honda Motor (7267.T), Fiat's (FIA.MI) Chrysler and Toyota Motor (7203.T), are affected by the regional recalls. They began in June in certain high-humidity areas of the United States after the National Highway Traffic Safety Administration (NHTSA) started investigating reports of air bag explosions in Florida and Puerto Rico.

The regional recalls initially affected nine automakers, but documents filed by Takata for a meeting this month with NHTSA and the affected companies listed GM for the first time as being potentially affected. The Takata documents, posted online this week by NHTSA, said the number of vehicles produced by the largest U.S. automaker was undetermined.

GM declined to comment.

Over the last six years, Takata has recalled 16 million vehicles globally for defective air bags, including the regional recalls.

Takata said on Friday the world's No. 2 maker of auto safety products was working to get the replacement inflator kits to its automotive customers. The September meeting documents included a forecast showing automakers had asked Takata to build almost 1.47 million inflator kits in the next six months.

That total was down about 39 percent from the August meeting's 2.39 million estimate, but Takata spokesman Alby Berman said the forecasts were not comparable. He said the August number included inflator kits required for recalls outside the United States, while the September estimate only pertained to kits required for the U.S. recalls.

NHTSA officials said they do not comment on ongoing investigations.

Prompted by NHTSA, Takata and automakers are seeking to determine whether exposure to high humidity caused any defect in the inflators collected though the regional recalls.

Takata said in the documents it may take three to four months after receiving enough of the recalled inflators before "we see patterns emerging in the data." Takata had received 4,109 of the recalled inflators for testing as of Sept. 15.

In the documents posted this week, Takata said it had faced production problems with the replacement inflator kits, because of a shortage of wire harnesses used in the part. Takata's Berman called that a "minor issue" and said it had been resolved.

Other automakers affected by the regional recalls include BMW (BMWG.DE), Ford Motor (F.N), Mazda Motor (7261.T), Mitsubishi Motors (7211.T), Nissan Motor (7201.T) and Fuji Heavy Industries' (7270.T) Subaru.