The National Highway Traffic Safety Administration issued a stern public warning, urging owners of vehicles covered by the Takata air bag recalls to “act immediately” in scheduling necessary repairs.

The recalls — issued as far back as 18 months ago and as recently as Oct. 20 — cover more than 7 million vehicles equipped with Takata air bag inflators, NHTSA said. The recalled vehicles are in the 2000-2008 model years.

The recalls involve multiple automakers, including Toyota, Honda, Mazda, BMW, Nissan, Mitsubishi, Subaru, Chrysler, Ford and General Motors.

"Responding to these recalls, whether old or new, is essential to personal safety and it will help aid our ongoing investigation into Takata airbags and what appears to be a problem related to extended exposure to consistently high humidity and temperatures,” said David Friedman, NHTSA deputy administrator. “However, we’re leaving no stone unturned in our aggressive pursuit to track down the full geographic scope of this issue."

The defective air bag inflators, linked to at least two confirmed deaths, can explode upon deployment. Metal fragments from the destroyed housing can disperse like shrapnel and injure vehicle occupants. The inflator propellant appears to be especially volatile and prone to such explosions in areas with absolute humidity – a measurement of water vapor in the air. (Relative humidity, in contrast, measures air moisture levels relative to the air temperature.)

As a result, NHTSA has stressed the need for immediate response by vehicle owners in Florida, Puerto Rico, Gulf of Mexico regions in Texas, Alabama, Mississippi, Georgia, Louisiana, Guam, Saipan, American Samoa, Virgin Islands and Hawaii.

At the request of Takata, some of the past recalls have been issued on a regional, rather than national, scale. Last week, two U.S. senators – Richard Blumenthal (D-Conn.) and Edward Markey (D-Mass.) criticized this strategy in a letter to Friedman. “Even if these cars are not actually registered in the particular states subject to the regional recall, they may nevertheless be driven there,” the letter stated. “Regional recalls that treat cars and trucks like they never leave their home make no sense.”

Blumenthal and Markey also raised questions about whether Honda has informed NHTSA of all death and injury claims associated with the air bag inflator defect. The senators cited research from the Center for Auto Safety.

Honda last month responded to similar questions by arranging for a third-party audit of its quarterly Early Warning Reports submitted to NHTSA, BusinessWeek reported.

Meanwhile, many dealers lack the air bag inflator replacement parts to accommodate the volume of recall repairs in the near future, according to multiple media reports. To learn whether their vehicle is covered by one of the recalls, vehicle owners can visit the appropriate automaker website and search by VIN.

Toyota this week advised affected vehicle owners to bring their vehicle to a Toyota or Lexus dealer, so the front passenger air bag inflator can be replaced with a new one. “If a replacement part is not available at the time of vehicle service, the dealer will follow procedures to temporarily disable the front passenger airbag assembly,” the automaker said. “In addition, the dealer will install a glove box hang tag informing occupants that the front passenger seat should not be occupied until the inflator assembly is replaced and the airbag is fully functional.”

Takata Corp., a major automotive supplier, is based in Tokyo. The company’s U.S. subsidiary, TK Holdings, operates out of Auburn Hills, Mich.

NHTSA posted the following list of vehicles covered by the recalls. The numbers, however, are subject to change since some vehicles may have been counted more than once.

BMW: 627,615 total number of potentially affected vehicles

2000 – 2005 3 Series Sedan

2000 – 2006 3 Series Coupe

2000 – 2005 3 Series Sports Wagon

2000 – 2006 3 Series Convertible

2001 – 2006 M3 Coupe

2001 – 2006 M3 Convertible

Chrysler: 371,309 total number of potentially affected vehicles

2003 – 2008 Dodge Ram 1500

2005 – 2008 Dodge Ram 2500

2006 – 2008 Dodge Ram 3500

2006 – 2008 Dodge Ram 4500

2008 – Dodge Ram 5500

2005 – 2008 Dodge Durango

2005 – 2008 Dodge Dakota

2005 – 2008 Chrysler 300

2007 – 2008 Chrysler Aspen

Ford: 58,669 total number of potentially affected vehicles

2004 Ranger

2005 – 2006 GT

2005 – 2007 Mustang

General Motors: undetermined total number of potentially affected vehicles

2003 – 2005 Pontiac Vibe

2005 Saab 9-2X

Honda: 5,051,364 total number of potentially affected vehicles

2001 – 2007 Honda Accord

2001 – 2002 Honda Accord

2001 – 2005 Honda Civic

2002 – 2006 Honda CR-V

2003 – 2011 Honda Element

2002 – 2004 Honda Odyssey

2003 – 2007 Honda Pilot

2006 – Honda Ridgeline

2003 – 2006 Acura MDX

2002 – 2003 Acura TL/CL

2005 – Acura RL

Nissan: 694,626 total number of potentially affected vehicles

2001 – 2003 Nissan Maxima

2001 – 2003 Nissan Pathfinder

2002 – 2003 Nissan Sentra

2001 – 2003 Infiniti I30/I35

2002 – 2003 Infiniti QX4 2003 – Infiniti FX

Mazda: 64,872 total number of potentially affected vehicles

2003 – 2007 Mazda6

2006 – 2007 MazdaSpeed6

2004 – 2008 Mazda RX-8

2004 – 2005 MPV

2004 – B-Series Truck

Mitsubishi: 11,985 total number of potentially affected vehicles

2004 – 2005 Lancer

2006 – 2007 Raider

Nissan: 694,626 total number of potentially affected vehicles

2001 – 2003 Nissan Maxima

2001 – 2004 Nissan Pathfinder

2002 – 2004 Nissan Sentra

2001 – 2004 Infiniti I30/I35

2002 – 2003 Infiniti QX4

2003 – 2005 Infiniti FX35/FX45

Subaru: 17,516 total number of potentially affected vehicles

2003 – 2005 Baja

2003 – 2005 Legacy

2003 – 2005 Outback

2004 – 2005 Impreza

Toyota: 877,000 total number of potentially affected vehicles

2002 – 2005 Lexus SC

2002 – 2005 Toyota Corolla

2003 – 2005 Toyota Corolla Matrix

2002 – 2005 Toyota Sequoia

2003 – 2005 Toyota Tundra