Blaming high costs, Mitsubishi said Wednesday it was exiting the projects, which planned 134 turbines to generate power for more than a million homes.

"The government regards offshore wind power as an important source of electricity towards making renewable energies (Japan's) main source of electricity, regardless of success or failure of a particular project," government spokesman Yoshimasa Hayashi told reporters.

The government "will further examine the issue, including reviewing conditions of the auction system, after examining factors behind the withdrawal from these projects," he added.

Japan declared in its updated energy plan this year that offshore wind power was a "trump card" in its drive to make renewables its top power source by 2040.

Japan is the world's fifth-largest single-country emitter of carbon dioxide, after China, the United States, India and Russia, and is heavily dependent on imported fossil fuels.

Nearly 70 percent of Japan's power needs in 2023 were met by power plants burning coal, gas and oil -- a figure Tokyo wants to slash to 30-40 percent over the next 15 years.

Wind power is meant to account for between four and eight percent in the same timeframe, up from around one percent now.

Almost 15 years after the Fukushima disaster, Japan is also turning back to nuclear power as it seeks to achieve carbon neutrality by 2050.