Japan's transport ministry says five vehicle makers have admitted to falsifying performance tests to get certification for their products.

The ministry says Toyota, Mazda, Yamaha, Honda and Suzuki all uncovered the misconduct while carrying out a government-ordered internal probe.

Ministry officials have ordered Toyota, Mazda and Yamaha to suspend some shipments for certain cars and motorbikes.

They have also instructed the firms to verify that the vehicles meet national safety standards.

Toyota says it will comply with the instruction.

Toyoda Akio, Chairman of Toyota Motor, told a news conference, "Acts like these undermine the very foundations of the certification system. As a manufacturer of automobiles, we believe they should never happen."

Yamaha and Mazda have already halted some shipments.

The ministry will send officials to conduct onsite inspections of all five companies.

The revelations follow similar cases of misconduct by Hino, Toyota Industries and Daihatsu in recent years.

The ministry responded to those cases by ordering 85 domestic automakers and parts companies to conduct internal checks, and report any inappropriate practices.