The world's third-largest economy is still heavily reliant on fossil fuels, in part because many nuclear reactors remain offline after the Fukushima meltdown a decade ago.

The documents released Wednesday by Japan's ministry of economy, trade and industry said the new target would make renewables the majority of the country's energy mix.

Greenpeace described the draft as "disappointing" and criticised Japan for "failing to commit to ending fossil fuel" despite setting a 2050 deadline for carbon-neutrality last year.

"The revision of the Basic Energy Plan is a pivotal point to demonstrate Japan's political will to achieve net-zero by 2050," Hisayo Takada, programme director at Greenpeace Japan, said in a statement.

"However, the draft plan is disappointing as it is not anywhere near sufficient to meet the 1.5 degrees Celsius target," Takada added, referring to the goal for global warming in the 2015 Paris agreement.

The draft policy left the ratio of nuclear energy unchanged at 20-22 per cent.

Thermal power supplies should account for 56 per cent, down from the present target of 41 per cent, it said.

The government aims to hold further discussions and finalise the policy in October, according to public broadcaster NHK.

In fiscal 2019, renewables accounted for 18 per cent of Japan's energy mix, with fossil fuels accounting for 76 per cent and nuclear power six per cent.