Toyota is doubling the number of pre-production redesigned Corollas it builds ahead of the model's introduction introduced in Japan this autumn, as part of efforts to ensure its quality, unnamed officials said.

Group unit Kanto Auto Works will produce 300 prototypes, compared with 150 it usually produces as trial cars, to make sure that the Corolla's 10th-generation model will be high in quality, the officials told Kyodo News.

The automaker recently announced it would delay the new Corolla's US debut a year until 2008 as the current model, which is built in North America, is still selling well as high petrol prices prompt buyers to switch to smaller, more fuel-efficient cars.

Toyota, which has been reeling from a series of vehicle defects in recent months, also plans to increase the number of pre-production cars built in other plants manufacturing the Corolla, the report said.

It is believed that the manufacturing cost of one pre-production vehicle is about 10m yen.

In recent years, Toyota has increasingly relied on computers to check mechanical problems, Kyodo News said.

But due to a recent rise in recalls, the Toyota group has apparently decided to get back to the basics of manufacturing by increasing opportunities for engineers to experiment with real cars, analysts told the news agency.