MILLINOCKET, Maine — The middle and high schools in Millinocket will probably be back in session Friday after two transformers exploded, forcing the schools to be closed late Thursday morning, officials said.

The interconnected Stearns High School and Millinocket Middle School lost power and were emptied when an electrical transformer on a nearby street, and then one on school grounds, blew out about 11:30 a.m.

The explosions damaged at least one power line running underground into one of the buildings, Superintendent Frank Boynton said.

“The second [explosion] took out at least one line,” Boynton said about 4:30 p.m. from a workshop he was attending in Augusta. “We are working to repair it now.”

Three underground power lines are being replaced. Exactly why the transformers blew is unknown, Boynton said, but several residents on Aroostook Street also lost electricity. The repair cost for the school transformer is unknown but will likely be “substantial,” Boynton said.

Rioux Electric Inc. and school workers expressed confidence that the repairs would be completed by midnight, but Boynton said parents and staff should follow snow day procedures on Friday morning and check television and radio listings to see whether school will be in session.

“We are pretty much being told we will be able to go to school tomorrow. If we can’t, and they run into more problems tonight, we will cancel school for the whole district tomorrow,” Boynton said. “We are going to be cautious.”

Too many staffers and parents run between the interconnected schools and the Granite Street School to make a partial shutdown workable, Boynton said.