Federal auto safety regulators Monday warned the owners of about 4.7 million vehicles with defective air bags made by Takata Corp. that they should "act immediately" to have them fixed.

The safety agency said it was particularly important for the owners of vehicles in states like Florida and Hawaii that have high humidity to act quickly in contacting auto dealers for fixes. Takata has told the safety agency it is concerned that the problem is more likely to occur in such a climate.

The unusual action indicates a heightened concern among regulators over the air bags, which are linked to at least two U.S. deaths. In a statement, the agency said its warning was prompted by new test results from Takata.

In regulatory filings, Takata has told the National Highway Traffic Safety Administration that the propellant – intended to burn quickly and produce gas to inflate the air bag – is defective. When a crash occurs, the propellant is too strong and can rupture its container, shooting metal parts at the driver or front-seat occupant.

The air bags are used in wide range of vehicles recalled over the past two years, including those made by Toyota, Honda, Mazda, BMW, Nissan and General Motors. The largest number, about 2.8 million, are made by Honda, followed by Toyota with 778,000.