The country's transport ministry found automakers had submitted incorrect or manipulated safety test data when they applied for certification of some vehicles.

The irregularities were also found in applications from Honda, Suzuki and Yamaha Motor, the ministry said.

The ministry asked automakers in late January to investigate vehicle certification applications following a safety test scandal at Toyota's Daihatsu car unit that emerged last year.

The ministry said it will conduct an on-site inspection at Toyota's central Aichi Prefecture headquarters on Tuesday.

Toyota, the world's biggest automaker by volume, said its wrongdoing occurred during six different tests conducted in 2014, 2015 and 2020.

In one example, it had measured collision damage on only one side of a model's hood while it was required to do so on both sides.

Toyota Chairman Akio Toyoda said, As the person responsible for the Toyota Group, I would like to sincerely apologize to our customers, car enthusiasts and all stakeholders for the problems that have occurred within the group.

I am truly sorry.

Toyota said it is still investigating issues related to vehicle fuel efficiency and emissions and aims to complete that inquiry by the end of June.

Mazda had suspended shipments of some models from last week after finding workers had modified engine control software test results, it said in a statement.

The scandals are proving to be a sore point for the government, which has otherwise earned praise from investors and executives for its corporate reforms.