The European Union's top environmental official warned his colleagues that automakers were rigging European emissions tests in 2013, long before the scam was uncovered last month, the Financial Times reported on Sunday.

One of the biggest scandals in the history of the automobile sector came to light after German carmaker Volkswagen admitted it had fitted 11 million of its vehicles with software designed to cheat official checks.

Top EU regulators were aware of test manipulation two years ago, but allowed regulatory loopholes to remain, according to the FT, which cited an exchange of letters between officials.

"There are widespread concerns that performance has been tailored tightly to compliance with the test cycle in disregard of the dramatic increase in emissions outside that narrow scope," EU environment commissioner Janez Potocnik wrote to industrial policy commissioner Antonio Tajani in February 2013, according to the newspaper.

US authorities in September accused Volkswagen of fitting vehicles with devices that switch on pollution controls when a car is undergoing testing, only to deactivate when it is on the road, allowing harmful levels of emissions.

The world's biggest carmaker by sales, Volkswagen has seen about half its value wiped off its shares since the news broke.

The once-respected automaker replaced its chief executive and faces billions of euros in potential legal costs and fines, as well as the costs of repairing vehicles, along with untold damage to sales and customer trust.

Investigations over rigging are underway in several countries including France, Germany, Italy, Spain and the United States.