Toyota Motor Corp. said Tuesday operations at all 14 of its group's vehicle assembly plants in Japan have been halted after a computer system failure earlier that it said was unlikely to have been caused by a cyberattack.

The world's largest automaker said later in the day that it hopes to resume production Wednesday, starting with 12 of the plants, as a "temporary measure."

While the scale of impact of the operation suspension is unclear, domestic output was above 10,000 units per day as of August last year, according to Toyota. Its domestic production includes cars for overseas exports.

A range of models has been affected in the latest incident, including small cars such as the Yaris and Corolla as well as the upscale Lexus brand.

Toyota said a malfunction in the "production order system" that occurred daytime Monday led 12 plants to halt from the morning of Tuesday and later to the suspension of the remaining two factories -- the Miyata plant in Fukuoka Prefecture and Daihatsu Motor Co.'s plant in Kyoto Prefecture.

The system processes orders for vehicle parts. The two plants were able to operate longer because they had parts in stock.

The incident seems to have exposed the vulnerability in Toyota's production method of avoiding holding excessive parts stock to efficiently manufacture cars.

In March last year, Toyota shut all of its domestic plants after its domestic supplier Kojima Industries Corp. suffered a system failure caused by a cyberattack.

The auto company was also forced to temporarily suspend part of its operations in July after a cyberattack on a computer system at the Port of Nagoya in Aichi Prefecture, a shipping hub for the company, disrupted port services for two and a half days.

In fiscal 2022, Toyota's world production reached 9.13 million cars, with 2.78 million made domestically.

Photo taken on Aug. 29, 2023, shows Toyota Motor Corp.'s Motomachi plant in Toyota in Aichi Prefecture, central Japan.  (Kyodo)
Photo taken from a Kyodo News helicopter on Aug. 29, 2023, shows Toyota Motor Corp.'s Motomachi plant in Toyota in Aichi Prefecture, central Japan. (Kyodo) 

Related coverage:

Hacker group attacks Japan nuclear websites over Fukushima water plan

Subaru to produce EVs in U.S. from 2027 to accelerate shift

Toyota profit doubles to record high as production recovers