A Japanese court on Tuesday issued a landmark injunction against the restarting of two atomic reactors, after the country's nuclear watchdog had given the green light to switch them back on.

The district court in the central prefecture of Fukui made the temporary order in response to a bid by local residents to halt the restart of the No. 3 and No. 4 reactors at the Takahama nuclear power plant, a court official said.

The Nuclear Regulation Authority (NRA) last December approved the restarting of the reactors, saying they met tougher safety standards introduced after Japan's tsunami-sparked nuclear disaster at Fukushima in 2011.

But "the safety of the reactors hasn't been secured", the court ruled, saying the watchdog's new standards were "lacking rationality", according to public broadcaster NHK.

The reactors could be damaged by an earthquake even smaller than that envisaged in the safety standards, the court said.

Plant operator Kansai Electric Power slammed the injunction as "extremely regrettable and utterly unacceptable" and said it would appeal against the decision.

A lawyer representing the plaintiffs called the ruling a "perfect victory".

"This is the best decision that we could have expected," he told supporters outside the courthouse.

Two other reactors at Takahama also remain offline.

Greenpeace hailed the court decision, saying it "could have a nationwide ripple effect on similar pending injunction cases -- threatening to derail the Japanese government's nuclear reactor plans".

A separate court ruling on the restart of two other reactors in southern Japan is expected later this month.

- 'Warning from the court' -

Hiroshi Miyano, a nuclear expert and visiting professor at Hosei University in Tokyo, said the court decision would affect the timing of future reactor restarts.

"This can be seen as a warning from the court, which told the (plant) operator that it has to better explain its resumption plans," Miyano said.

"But it does not mean the possibility of their resumption has disappeared," he added, saying the utility may still be able to convince the court that the reactors could withstand a quake.

The government's top spokesman Yoshihide Suga said Tokyo "respects" the watchdog's earlier approval to turn on the reactors, but did not comment directly on the court ruling.

"There is no change in our policy to go ahead with resuming (nuclear) operations," Suga added.

Pro-atomic Prime Minister Shinzo Abe has backed an industry push to return to nuclear -- which once supplied more than one quarter of Japan's electricity -- as a plunging yen sent the country's energy import bill soaring.

But Japan has seen a groundswell of public opposition to the technology since Fukushima, where reactors went into meltdown after a tsunami swamped their cooling systems -- setting off the worst atomic disaster since Chernobyl in 1986.

Japan's entire stable of nuclear power stations was gradually switched off following the disaster, while tens of thousands of people were evacuated due to concerns about radiation exposure.

Many are still unable to return to their homes and scientists have warned that some areas around the plant may remain uninhabitable for decades or more.

mis-kh-si/pb/sm

Kansai Electric Power