Japanese officials have raided an office of Mitsubishi Motors following the revelation that the carmaker had falsified its fuel economy data, BBC News reports.

The officials searched its plant in the central Japanese city of Okazaki.

Mitsubishi has admitted that employees altered data to flatter mileage rates on more than 600,000 vehicles.

A government spokesman said they were treating it as an "extremely serious case" and that it had ordered the company to submit a full report.

The authorities have set 27 April as the deadline for Mitsubishi Motors to hand over the report on the inaccurate testing.

Japan's chief cabinet secretary, Yoshihide Suga, said: "Based on [the findings from] the raid, and a report from the company, we would like to reveal the extent of the inaccuracies as soon as possible.

"We will deal with the situation in a strict manner and would like to make sure of the safety of cars."

The raided office is the company's second largest plant in Japan and is a manufacturing hub as well as a research facility.