Tokyo (CNN) -- Japan restarted nuclear power production Sunday for the first time since shutting down all the country's reactors in the wake of the Fukushima Daiichi meltdown after last year's devastating tsunami.
Kansai Electric Power Co. Ltd. (KEPCO) began an operation to restart the Ohi nuclear plant's No. 3 reactor on Sunday night, it said, despite protests from raucous demonstrators at the site.
Dancing, chanting, and singing , throngs of demonstrators had converged outside the nuclear power plant earlier on Sunday, decrying the scheduled relaunch.
A line of shield-wielding police contained the protesters outside Ohi, where demonstrators chanted: "Opposition to restart!"
The process of starting a nuclear reactor takes hours, starting with the removal of control rods to allow a chain reaction to begin.
The reactor is due to start providing some electricity to western Japan -- which includes Osaka, Japan's second-biggest city -- by Wednesday. Ohi's No. 4 reactor is scheduled to resume operations by July 24.
All 50 commercial nuclear reactors in Japan have been offline since May 5 for safety checks. The government has been conducting simulation tests for restarting its nuclear reactors in response to public concerns over their safety in the wake of the Fukushima Daiichi crisis last year.
Before the March 2011 nuclear disaster, Japan had relied on nuclear energy for about 30% of its electricity needs, according to government figures.
Though no deaths have been attributed to the nuclear accident, the earthquake and tsunami killed more than 15,000 people in northeastern Japan. The damaged Fukushima spewed radiation, prompting the government to evacuate tens of thousands of people.
CNN's Elizabeth Joseph contributed to this report.