CAMBRIDGE - A series of subterranean explosions in Harvard Square early this morning which sent flames shooting out of manholes have been extinguished, police and fire officials said.

No injuries have been reported from the four to five explosions, which were triggered by an electrical cable that malfunctioned, said NStar spokeswoman Caroline Allen.

The fires were put around 8:30 a.m. No damage has been reported to stores in the area. Investigators are on the scene examining the underground network of wires.

One line of traffic has been cleared on Massachusetts Avenue from the Cambridge Common into Harvard Square. Traffic has been rerouted onto Mount Auburn Street. Police said they hope to have one lane open on Mass. Avenue from Harvard Square toward Central Square by noon.

Dunster, Holyoke, and Plympton Streets up to Putnam Street are still blocked off in Harvard Square, officials said.

The Cambridge Fire Department has been on the scene since 2:30 a.m. said James F. Burns, deputy Cambridge fire chief. He said there was an explosion in the underground utility tunnel and a lubricating oil caught fire. He said the oil provided the fuel for flames which jetted out of a manhole, shooting ten feet into the air. He said the strategy was to let the fire burn itself out.

Burns said they have now flooded the electrical conduit tunnel with water to cool it down and prepare it for investigators and utility workers to go underneath to start repairs.

A dispatcher for the MBTA said Red Line subway service through Harvard Square was not affected by the fire, but three bus routes are being diverted

The cable malfunction was akin to a house blowing a fuse, but on a much larger scale, Allen said. The initial blast knocked out power to 700 customers. But much of the power has been restored.

The explosions were centered near Massachusetts Avenue and Dunster Streets, but the flames spread through the underground network of manholes.

Harvard University classes were not disrupted, but the Holyoke Center is closed.