TOKYO (Reuters) -Toyota Motor said on Monday its chairman would speak about an investigation it has conducted into its vehicle certification applications after being prompted by Japan's transport ministry.

Chairman Akio Toyoda will hold a press conference at 0800 GMT on Monday, the company said.

The transport ministry said separately it will conduct an on-site inspection at Toyota's headquarters on Tuesday.

It said irregularities were found in applications to certify models from Toyota, Mazda Motor, Yamaha Motor, Honda Motor and Suzuki Motor and that it had ordered Toyota, Mazda and Yamaha to suspend shipments of some vehicles.

The ministry had requested automakers to investigate their vehicle certification applications following a safety test scandal at Toyota's compact car unit Daihatsu.

Toyota said on Monday it has temporarily halted shipments and sales of three car models made in Japan. Yamaha said it had halted shipments of a sports motorcycle.

A Mazda spokesperson said it would issue a press release at 0650 GMT where it would detail its response, followed by a press conference at 0700 GMT.

Honda is also due to hold a press conference later in the day.

A Toyota spokesperson added that the company is still investigating issues related to vehicle fuel efficiency and emissions, and aimed to complete the inquiry by the end of June.

Toyota shares closed down 1.8%.

The company said it had provided inadequate data in pedestrian and occupant protection tests for three production models - the Corolla Fielder, Axio and Yaris Cross - and errors in crash tests and other test methods for four discontinued models, including one sold under the Lexus luxury brand.

It added there were no performance issues that violated regulations and customers did not need to stop using their cars.

In the Daihatsu scandal, a panel found that the unit had rigged side-collision safety tests carried out for 88,000 small cars, most of those sold as Toyotas.