The Hiroshima High Court on Wednesday revoked a lower court decision and ordered the suspension of a nuclear reactor in western Japan, dealing a blow to the government and utilities aiming to bring more reactors back online.

The first high court suspension order in a series of similar injunction requests demanded that plant operator Shikoku Electric Power Co. shut the No. 3 unit of the Ikata power plant in Ehime Prefecture until the end of September next year.

The ruling blocks the planned resumption in January of the unit, which is currently offline for a regular checkup after it was restarted in August 2016.

Shikoku Electric said the decision is "unacceptable" and plans to file an appeal against it.

The court found it was irrational that the Nuclear Regulation Authority judged that the potential risks associated with a volcanic eruption would not breach the stricter regulations introduced following the 2011 Fukushima nuclear crisis.

"Specific threats to the lives and health of residents are anticipated," the court said.

The latest decision follows the ruling by the Otsu District Court in March 2016 that ordered Kansai Electric Power Co. to suspend two reactivated nuclear reactors at the Takahama plant. The district court decision was later overturned by the Osaka High Court.

The government is looking to produce 20 to 22 percent of the country's electricity supply with nuclear power by 2030 after the Fukushima nuclear crisis led to a nationwide halt of nuclear plants.

The focal points of the latest decision included whether the estimate by the plant operator of the potential size of an earthquake, a key factor in a reactor's quake-resistance design, was reasonable, and whether safety screening conducted under the new regulations was credible.

The plaintiffs claimed that in calculating the size of a potential earthquake, the utility underestimated the fact that the reactor lies above the epicenter of an anticipated Nankai Trough mega-quake and that it is located near a geological fault.

They added that the post-Fukushima regulations cannot ensure safety and major damage could occur at the time of an accident or disaster because they were compiled without thoroughly determining the cause of the 2011 disaster.

But Shikoku Electric said that it has ensured safety and there is no danger.

Hiroyuki Kawai, the lawyer representing the plaintiffs said, "Our plea was understood. We could protect the Seto Inland Sea. It is our victory."

The plaintiffs had said that if the Ikata plant, which faces the Seto Inland Sea, was to be severely damaged, nuclear substances could spread and contaminate the sea.

In March, the Hiroshima District Court had found that the new regulations and Shikoku Electric's estimates of a possible earthquake and tsunami were reasonable.

The district court had turned down the request to halt the reactor, saying, "There is no specific risk that residents will suffer severe damage due to radioactive exposure associated with an accident."

Following the checkup, Shikoku Electric was expected to bring the reactor back online on Jan. 22.

The plaintiffs were four residents from Matsuyama in Ehime and Hiroshima on the other side of the Seto Inland Sea. Similar injunction demands have been contested at the Takamatsu High Court, the Oita District Court and the Iwakuni branch of the Yamaguchi District Court.