UPDATE, 6:17 p.m.: The is no word on what caused the fire but it remains under investigation, according to WBZ-TV. UPDATE 12:50 p.m.: Waltham firefighters have the fire on Prospect Street Avenue knocked down, said Waltham Fire Chief Paul Ciccone. They are just putting out hot spots. The cause is still not known, Ciccone said.
The fire damaged the roof and some of the interior rooms on the second floor, he added.
Prospect Street is closed in both directions near the Hess gas station.
UPDATE: The fire damaged the roof and upper floor area of the multi-family home. Newton, Waltham, Cambridge and Weston firefighters are all on the scene.
UPDATE 11:45 a.m.: A third alarm has been struck. --- Waltham firefighters are responding to a two-alarm fire at 17 Prospect Ave., according to the Waltham Fire Department.
Firefighters have moved from interior attack operations to exterior operations.