Three oil fields in the central Sumatran province of Riau with a combined output of 400,000 barrels a day have been halting oil production since late Thursday after lightning struck power transformers and obstructed the supply of power to the three fields, an official said Friday.

Two of the fields are the Duri and Minas fields, operated by Chevron, and have a combined output of 379,000 barrels a day. The other is a 21,000-barrel-a-day field operated by PT Bumi Siak Pusako, which is controlled by the Riau government. Bumi's field uses electricity generated by Chevron's power plant in Duri.

"Our production has been halted since yesterday," said an official at Bumi Siak Pusako, declining to be named.

The disruption has dealt a blow to the government's target of producing 977, 000 barrels of crude per day this year.