Mitsubishi Heavy Industries said Monday it would postpone delivery of its long-awaited regional jet by two years, and warned over soaring development costs for the problem-plagued plane.

This is the fifth time that the company has pushed back the commercial rollout of its Mitsubishi Regional Jet (MRJ), Japan's first domestically produced passenger plane for over half a century.

The decision to move back the first customer delivery to mid-2020 from mid-2018 comes after local media reports said the plane needed more design changes to ensure it was safe.

The problem was linked to the location of certain electronic equipment, the Nikkei business daily and other Japanese media reported.

The company said it was modifying the design of "electrical configurations" to meet the latest safety standards, which have become more and more strict given the threat of terrorism.

"We now have to think of risks that are unthinkable in the normal course of things, such as a massive flood of water damaging electrical systems or a bomb explosion destroying those systems," Nobuo Kishi, vice president of the firm's aviation unit, told a press briefing in Tokyo.

Development costs could come in as much as 40 percent higher than an original range of between 150-180 billion yen ($1.3-1.6 billion), the firm said, citing stricter safety standards.

The development of the MRJ has suffered a series of delays, largely owing to software upgrades and other design changes.

The original plan when the programme started in 2008 was for the first customer delivery to begin in 2013.

The twin-engine MRJ marks a new chapter in the country's aviation sector, which last built a commercial airliner in 1962 -- the YS-11 turboprop that was discontinued about a decade later.

After initially being barred from developing aircraft following World War II, Japan -- and its MRJ jet -- is competing with other passenger jet manufacturers such as Brazil's Embraer and Canada's Bombardier.

Mitsubishi unveiled the jet -- which is about 35 metres (115 feet) long and seats about 80 passengers -- in October 2014 and has received more than 400 orders.

The short-to-medium-haul plane was backed by the Japanese government and a consortium of major firms including Toyota.

Last year, the new passenger jet completed a flight to the United States for testing, after aborting two earlier attempts.

The company's Tokyo-listed shares slipped 1.59 percent to close at 524.1 yen ($4.60)