Japan is becoming nuclear power-free as the last remaining reactor in operation has begun shutting down amid controversies surrounding atomic power.

The temporary move has started as the Kansai Electric Power started disconnecting power from the No 4 nuclear reactor, the only operating unit among Japan's 50 reactors.

The process is expected to take several hours before the plant gradually stops generating power for regular maintenance work.

It is still unclear when the plant will resume operations. The inspections usually take about four to six weeks, but resumption of work largely depends on the political atmosphere.

Many Japanese oppose the use of atomic energy following the Fukushima disaster, although Prime Minister Shinzo Abe remains largely in support of nuclear power.

The Abe administration had voiced serious concern that the world's third-largest economy will plunge into darkness if atomic energy is entirely phased out.

Nuclear power has accounted for nearly one third of Japan's electricity needs and had come to a halt following the crisis in 2011. Japan is looking to exploit fossil fuel sources as an alternative to nuclear power.

This will be the third time since Japan has gone fully nuclear-free - in 1970 and again in mid-2012.

"Safety is important, but if you waste time, that too has an effect on safety. The Fukui nuclear power plant sites have a long history and respond to risks. My position is therefore different from other prefectural governors," said Fukui Governor Issei Nishikava.

Scores of nuclear power operators had asked for approval to reopen the reactors following their closure. But industry regulators have been concerned by the extent of the Fukushima disaster.

"The argument that no nuclear power dents the economy would be myopic, considering that if by mistake we had another tragedy like Fukushima, Japan would suffer from further collateral damage and lose global trust. In the new economy, the less you use energy, the more value-added you become. The big chorus for nuclear power is hampering the efforts to move to a new, more open economy," Tetsunari Iida, chief of the Institute for Sustainable Energy Policies, told Reuters.

The tsunami and earthquake in March 2011 damaged the Fukushima nuclear power plant causing a meltdown of nuclear fuel rods in three reactors. This has caused widespread contamination of air and sea.