More than 15 familes were left homeless last night after a sevenalarm fire gutted two Cambridge St. apartment buildings.

The fire reduced the two turn-of the-century-buildings at 1413 and 1433 Cambridge St. to rubble, creating a dense cloud of smoke that could be seen as far away as Eliot House.

As a crowd of about 200 gathered to watch the blaze, residents stood in front of their former homes crying tears of shock and disbelief.

"Everyone lost everything that they owned," said Jackie McCarthy, a 32-year resident of 1431 Cambridge St.

One civiliian and one police officer were injured in the blaze, neither seriously, according to Deputy Gerald Reardon of the city Fire Department. They were taken to Cambridge Hospital, he said.

The cause of the fire was still unknown last night, he said.

The fire broke out at about 8:10, according to Raphael Mendel, an auxiliary firefighter.

"When I got here at 8:30, it was roaring," he said.

More than 20 engines responded to the fire, including several from the Boston fire Department.

The buildings were still blazing at 10 p.m., and Reardon estimated that they would burn for another hour.

"The fire started outside and worked its way up between both buildings," said Reardon. "It's very unusual that a fire takes of that quickly."

One house on Line St., behind the Cambridge St. buildings, caught fire as well.

The firefighters, however, were able to put that fire out fairly easily, Reardon said.

Reardon estimated that between 15 and 20 families lost their homes in the blaze.

Smoke from the fire could be smelled throughout the Square last night.

At the Kennedy School of Government on JFK St., a speech by ABC News correspondent Cokie Roberts was interrupted when smoke filed the room. An audience member said people feared that the Kennedy School was on fire.