At least 335,000 homes and businesses were left without electricity after a blackout hit Kediri municipality and Kediri and Tulungagung regencies in East Java on Tuesday.
Ustriadi, from the local office of state-owned power monopoly PT PLN, said there had been a 1,000-kilovolt-ampere loss in the affected areas for unknown reasons.
He added the company apologized to the public for the blackout.
Ustriadi said he did not know how long the blackout would last, as the company was investigating the incident.
PLN is now seeking to divert power from the neighboring Mojokerto and Blitar regency grids.