Prime Minister Yoshiko Noda said the restarts at the Oi nuclear power plant, in central Fukui prefecture, were necessary to avert power shortages.

It will take up to six weeks to get the reactors fully operational, the plant's operators said.

Noda made the announcement at a cabinet meeting following the approval of Fukui Governor Issei Nishikawa.

Japanese authorities ordered the closure of all of the country's 50 reactors for maintenance or safety checks after a powerful earthquake and tsunami triggered a meltdown at the Fukushima power plant in March 2011.

Japan relied on nuclear power for about 30 percent of its energy needs before the shutdowns.

The decision to restart the Oi reactors comes amid widepread public concern about nuclear safety.

Hundreds demonstrators gathered outside Noda's office on Friday to protest the move.

According to a poll by Mainichi Daily News newspaper, more than 70 percent of the public opposes restarting the reactors.