The world's fourth-largest economy is targeting carbon neutrality by 2050 but remains heavily reliant on fossil fuels -- partly because many nuclear reactors were taken offline after the 2011 Fukushima meltdown.

The government now plans to increase its reliance on nuclear power, in part to help meet growing energy demand from artificial intelligence and microchip factories.

The 60-year limit was brought in after the 2011 disaster, which was triggered by a devastating earthquake and tsunami in northeast Japan.

Under the amended law, nuclear plants' operating period may be extended beyond 60 years -- in a system similar to extra time in football games -- to compensate for stoppages caused by "unforeseeable circumstances", the government says.

This means, for example, that one reactor in central Japan's Fukui region, suspended for 12 years after the Fukushima crisis, will now be able to operate up until 2047 -- 72 years after its debut, the Asahi Shimbun daily reported.

But operators require approval from Japan's nuclear safety watchdog for the exemption. The law also includes measures intended to strengthen safety checks at ageing reactors.

The legal revision is also aimed at helping Japan better cope with power crunches, after Russia's invasion of Ukraine sparked energy market turmoil.

Japan's Strategic Energy Plan had previously vowed to "reduce reliance on nuclear power as much as possible".

But this pledge was dropped from the latest version approved in February, which includes an intention to make renewables the country's top power source by 2040.

Under the plan, nuclear power will account for around 20 percent of Japan's energy supply by 2040 -- up from 5.6 percent in 2022.

Also in February, Japan pledged to slash greenhouse gas emissions by 60 percent in the next decade from 2013 levels, a target decried by campaigners as far short of what was needed under the Paris Agreement to limit global warming.

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