ALBANY - Several underground explosions forced National Grid to cut the power in Troy, a city engineer said Sunday.

Russ Reeves said no one was injured in the blast, which sent manhole covers flying about 15 feet in the air 4 a.m. Sunday.

“Thank God it occurred in the early morning and not in the daytime hours, because there's no question people would have been killed,” he said.

An electrical short caused a fire, which built up pressure underground, causing the explosion, Reeves said. But National Grid officials said they had not determined what caused the fire.

“Our first priority is to fix the damaged equipment and restore power to the area,” spokesman Patrick Stella said. National Grid worked with emergency personnel to secure the area.

The blast blew out windows in about 15 buildings.

“Over a 50 year period there has been manhole fires and explosions, but nothing to this extent,” Reeves said. “This is quite rare.”

The explosion was not related to any dangerous gases, but did cause a minor natural gas leak in the area, Reeves said. It was contained later Sunday.

At the peak, between 20 and 30 customers had no power, but by late Sunday Stella said just two buildings were without power. Those were expected to be restored early Monday.

Reeves said city engineers would meet with National Grid and fire officials in the next week to discuss how to reduce the risk of the same thing happening again.

“We're going to prevent this from happening again,” He said, “Thank God no one was hurt.”