The Boston Fire Department responds to the scene of an explosion at the NStar substation in Allston early this morning. The explosion, occurring around 11 p.m. last night, could be seen from Harvard Square.

An explosion at an NStar power substation in Allston late last night sent flames shooting 75 to 100 feet in the air, according to the Boston Fire Department (BFD).

The explosion caused power outages for about 10,000 NStar customers, although most outages were only momentary, said NStar spokesperson Mike J. Monahan. All customers had their power restored by 1:30 a.m. this morning.

There were no injuries reported as of early this morning.

The explosion, about three blocks from the edge of Harvard’s Allston land holdings, occurred around 11 p.m., although there were conflicting reports of whether there was a second explosion.

“It sounded like lightning. I saw two explosions about five minutes apart or so,” said Jennifer Chin, a resident of Mansfield Street, directly behind the substation.

“I was watching TV and the lights flickered, they came back and it was horrifying. I saw a mushroom cloud of fire. I went outside and saw a whole bunch of people running [toward the blaze],” said Allston resident Ajda Snyder.

Numerous BFD and rescue units responded to the scene at NStar’s 288 Lincoln St. substation.

BFD District 11 Chief Patrick J. Ellard said that the fire was no more than a two-alarm incident, but that extra units had been called in because of the oil and gas at the scene.

The fire only took BFD about five minutes to extinguish, he said.

By midnight last night, most fire units had left the scene and the remaining fire crews were watching NStar’s built-in sprinklers water down the charred transformer.

Although NStar officials had not determined a cause by early this morning, Ellard said he suspected that the rain and snow last night contributed to the explosion.

“We don’t know why yet. Our first priority is getting people back on-line,” Monahan said.

The explosion was visible at least as far as the Radcliffe Quad.

Harvard students who saw the explosion out their windows reacted with horror—and quickly sent e-mails to House open lists asking for further information.

“My first thought was it’s the apocalypse—they have bombed the Business School,” said Adams House resident Adrienne A. Polich ’03.

“It looked like a bomb had dropped. The whole sky was electric orange,” another Adams resident Michaela O. Daniel ’03 said. “From our window it looked like the Business School had exploded.”

This is the third explosion at the location in two years. Last August, gas in sewers outside the plant ignited, and in June 2000, a transformer at the site exploded, showering nearby residences and cars with oil. That fire burned for about an hour before burning itself out.

—Joseph P. Flood, David H. Gellis, Garrett M. Graff, Andrew S. Holbrook, Jeslyn A. Miller and Jenifer L. Steinhardt contributed to the reporting of this article.

—Staff writer Ronaldo Rauseo-Ricupero can be reached at rauseo@fas.harvard.edu.