Automakers recalled a record 51.26m vehicles in the US in 2015, continuing a historic surge for car companies facing an unprecedented government crackdown on safety lapses, a media report said.

The total topped the 50.99m vehicles recalled in 2014, regulators told the Wall Street Journal.

The recalls in each of the past two years surpass any annual total logged by federal regulators in nearly five decades.

The WSJ noted the 2014 figure was revised downward from 64m, in part due to changes in counting recalls linked to rupture-prone air bags made by Takata. Recalls began surging that year as General Motors faced questions over defective ignition switches now linked to 124 deaths, and as nearly all car makers were affected by Takata air bags.

"Clearly, massive recalls are still a prominent part of the safety landscape," Mark Rosekind, head of the National Highway Traffic Safety Administration, said at the Washington auto show.

"Part of what's happened is a vigilance in looking for defects and getting them addressed," Rosekind told the WSJ. He said it would take a couple of years to see whether carmakers had become consistently proactive in addressing safety problems.

Rosekind on Thursday detailed a new, year long, online-advertising campaign from regulators aimed at encouraging consumers to use a government VIN database to spot open recalls and to prod them to quickly get repairs. About 25% of U.S. owners of recalled vehicles never get free repairs, according to automakers.

The campaign comes after car makers vowed last week, in a meeting with government officials in Detroit, to better alert regulators to defects, fix recalled vehicles faster and improve cybersecurity. Some lawmakers and safety advocates criticised the agreement for lacking penalties if car makers don't improve. Rosekind told the WSJ voluntary measures are preferable to enforcement and emphasised that chief executives of car makers had gathered together to discuss safety for the first time at a December summit with regulators in Washington.

"We support education efforts beyond what automakers are already doing to increase the consumer participation rate, and we urge consumers to regularly check NHTSA's website to find out if their vehicle has open recalls," said the Alliance of Automobile Manufacturers, a Washington lobbying group representing a dozen car companies, including GM and Fiat Chrysler Automobiles.

The WSJ said the outsize recall total in part traces to more than 19m vehicles equipped with rupture-prone Takata air bags linked to nine deaths. A dozen car makers are recalling the vehicles.

Regulators have ramped up oversight after facing criticism from lawmakers and others for failing to better police auto companies, the report noted. A government audit last year found regulators too often relied on automakers to report safety defects, culminating in a failure to spot GM's defective switch.

Car makers, meanwhile, are recalling more vehicles than ever to get ahead of government investigations and attempt to stem criticism from government officials and others for dithering on safety problems. GM in September agreed to pay a $900m penalty to settle a Justice Department probe of its defective switches and admitted to misleading regulators and consumers.

The WSJ said Fiat Chrysler is among the automakers bearing the brunt of regulators' increased scrutiny. The company in 2015 recalled more than 11.5m vehicles, more than any other car maker, according to government data. About 4m were on account of Takata air bags. Another 1.4m were recalled after hackers commandeered a moving Jeep's controls from a laptop miles away, though nobody was injured.

The company in 2015 suffered significant fines for lapses with recalls covering millions of vehicles, including older Jeeps with rear petrol tanks linked to dozens of fatal fires. Regulators fined Fiat Chrysler again in December for failing legal requirements to report deaths, injuries, warranty claims, consumer complaints and other information to help regulators spot possible safety problems that could need a recall.

Fiat Chrysler in a statement pointed to recent overhauled safety practices, including hiring more people and rolling out an Internet portal that consolidates recalls to help dealers assist customers.

The WSJ said Honda, which also faced a fine for safety-reporting lapses at the end of 2013, recalled roughly 11m vehicles last year, according to government data. The automaker's increased recalls are largely due to Takata air bags. A Honda spokesman told the Journal many Takata airbag inflators in the total were subject to repair under previous actions in 2014. Only about 3m vehicles in total from Honda and Acura "were newly subject to recall repair in 2015", the spokesman said.