An extensive blackout struck Tokyo on Wednesday, affecting government offices and halting trains in the Japanese capital just before the evening rush hour.
Tokyo Electric Power Co., a utility serving the Tokyo region, said officials are investigating the cause of the blackout.
The company, known as TEPCO, said smoke was detected at its unmanned power substation in Niiza city, near Tokyo, and officials are looking into whether it's related to the blackout.
TEPCO said as many as 350,000 households and offices were temporarily out of power. Electricity was restored to most of them later.
Japanese television showed black smoke billowing from the substation in a business district. There were no immediate reports of injuriest. Tokyo's metropolitan police department, the land and transportation ministry and the foreign ministries were among the government offices that briefly lost power.
The Tokyo Fire Department said they received reports from people trapped inside elevators in downtown Tokyo and were assessing the situation. Traffic lights were also temporarily out in some locations in Tokyo.
Chief Cabinet Secretary Yoshihide Suga told a news conference that officials are looking into the cause of the incidents, but did not answer when asked about a possible sabotage, according to NHK.