Japan will Tuesday begin restarting its nuclear power programme, officials said, after a two-year shutdown sparked by public fears following the Fukushima crisis.

The restart comes more than four years after a quake-sparked tsunami triggered meltdowns at the Fukushima plant, prompting the shutdown of Japan's stable of reactors in the world's worst atomic crisis in a generation.

Resource-poor Japan, which once relied on nuclear power for a quarter of its electricity, restarted two reactors temporarily to feed its needs. But they both went offline by September 2013, making it completely nuclear-free for about two years.

Japan has ushered in tougher safety rules to avoid a repeat of Fukushima, including more backup prevention measures and higher tsunami-blocking walls in areas most susceptible to them.

The government of Prime Minister Shinzo Abe is keen to get some of about four dozen reactors back up and running. So are the power companies that own them, fed up with having to make up lost generating capacity with pricey fossil fuels.

"It is important for the country's energy policy that the government go ahead with reactor restarts once they are confirmed as safe," top government spokesman Yoshihide Suga told reporters Monday.

"The biggest priority is safety."

The reactor No. 1 at the Sendai nuclear plant, nearly 1,000 kilometres (620 miles) southwest of Tokyo, has been loaded with atomic fuel. Its operator announced Monday the reactor would be switched on by 10:30 am (0130 GMT) Tuesday.

The 31-year-old reactor was expected to reach full capacity by "around 11:00 pm" Tuesday and would start generating power by Friday.

But regular operations would not begin until early September, a Kyushu Electric Power spokeswoman said.

- Stricter rules -

Several other reactors have received a safety green light from officials, who stressed that any switched-on reactor would operate under much tighter regulations than those that existed before Fukushima, the worst atomic disaster since Chernobyl in 1986.

"A disaster like that at Tokyo Electric Power's Fukushima Daiichi nuclear plant will not occur," under the new rules, Nuclear Regulation Authority chairman Shunichi Tanaka said in an interview with the Nikkei newspaper published at the weekend.

"The new regulations are incomparably (stricter) than those under the old system."

Tanaka conceded there was "no such thing as absolute safety", but said any future crisis would "be contained before it reached a scale anywhere near what happened in Fukushima".

But Japan's people are sceptical and the country remains deeply scarred by Fukushima, which forced tens of thousands of people from their homes -- many of whom will likely never return.

On Monday about 400 protesters rallied in front of the Sendai plant, which is on the southern tip of Japan's Kyushu island.

"I can never tolerate this," one demonstrator told local television.

"I cannot stand they are resuming the reactor when the Fukushima nuclear accident remains far from being solved."

While the government has been pushing for increased use of solar power and other reneweables, Ai Kashiwagi from Greenpeace Japan called for more to be done.

"The government still remains committed to an economy based on nuclear and fossil fuel energy, but the reality is that Japan has the potential to generate 56 percent of its electricity from renewable resources by 2030," Kashiwagi said.

Last month the central government notified Naraha, a town in the Fukushima region, that it would lift the evacuation order in place since the 2011 disaster.

Its 7,400 citizens will be the first evacuees to be able to return home permanently, among seven municipalities where the entire population was ordered to leave.

However, Naraha evacuees have mixed feelings about going home due to concerns over radiation and lack of medical care, and it was not clear how many of them would return.

The compensation bill for Fukushima, separate from the cash necessary for decommissioning the reactors, has reached at least $57 billion and is expected to increase.