The announcement came after an independent panel also found the malpractice dated back to 1989, when the oldest instance was confirmed and reports said the firm faced on-site inspections by government officials.

The logo of Japanese automaker Daihatsu is seen during the press day of the Japan Mobility Show in Tokyo on October 25, 2023. Toyota subsidiary Daihatsu said on Deember 20 it will suspend shipments of all car models in Japan and abroad, following news it had rigged safety tests. Kazuhiro NOGI / AFP

Toyota, the world's biggest carmaker, expressed its "sincere apologies" over the issue and said it would carry out "a fundamental reform".

The panel was set up earlier this year to probe a safety scandal that emerged in April.

The investigation "found new irregularities in 174 items within 25 test categories" in addition to wrongdoing previously detected in April and May involving door parts and side-collision tests, Toyota said.

With certification being a "major prerequisite" for an automobile manufacturer to conduct business, "our misconduct that surfaced this time amounts to disregard" of that very process, Daihatsu president Soichiro Okudaira told reporters, before bowing deeply to apologise.

In a statement, Toyota also recognised the "extreme gravity" of Daihatsu's neglect, which has "shaken the very foundations of the company as an automobile manufacturer".

"Daihatsu decided today to temporarily suspend shipments of all Daihatsu-developed models currently in production, both in Japan and overseas," the auto titan said in a statement.

The panel of outside experts attributed the decades-long irregularities in part to "an excessively tight and rigid development schedule".

Daihatsu employees were "exposed to the intense pressure to pass crash tests on their first attempt" to minimise the number of vehicles destroyed and thereby "reduce costs", committee chair Makoto Kaiami told reporters.

"'No failure can be forgiven' -- that was the kind of mindset," he said.

With the latest findings, the number of car models linked to wrongdoing now totals 64, including some sold under the Toyota brand which will also be suspended.

The firms said it was unaware of any accidents that have arisen from the falsification, but "thorough technical verification" was underway.

Public broadcaster NHK reported that Japan's transport ministry will conduct an on-site inspection of Daihatsu on Thursday.

The independent panel also blamed Daihatsu's misconduct on the lack of expertise by managers and its opaque work environment.

"Even if irregularities or deceptions were committed, they would not be detected," the report said.

In April, Daihatsu admitted falsifying crash test results for four of its models, involving a total of 88,000 vehicles manufactured in Thailand and Malaysia in 2022 and 2023.

Then in May, it announced it was halting production in Japan of two hybrid vehicle models because of similar "irregularities", including the Toyota Raize SUV, manufactured on behalf of its parent company.

"We believe in order to prevent recurrence, in addition to a review of certification operations, a fundamental reform is needed to revitalise Daihatsu as a company," Toyota said.

Founded in 1907 to manufacture internal combustion engines, Osaka-based Daihatsu launched its first three-wheeled vehicle in 1931, before being taken over by Toyota in 1967.