NASHUA - Between 50 and 75 occupants of a three-story apartment building were evacuated Wednesday when a fire broke out around 7:30 a.m. at Boulder Park Apartments.

Fire officials say the blaze, which began in the ceiling of a second-floor bathroom at 18 Kessler Farm Drive, was likely caused by an electrical malfunction. It does not appear to be suspicious, said deputy fire chief Kevin Kerrigan.

"It is still under investigation," he said Wednesday afternoon. "We are very lucky that the fire wasn't earlier in the morning."

The occupant of apartment 635 was awake and noticed the fire, according to Kerrigan, who said although several people had already left for work, there were still many residents of the multi-unit apartment building at home.

"That is a very big building," he added. "It could have been much worse."

When fire crews arrived on the scene, smoke was visible from the outside of the building. Firefighters were able to extinguish the blaze quickly, confining it to the bathroom, said Kerrigan. People were still inside the building when firefighters arrived, and several occupants were assisted from the apartment complex through heavy smoke conditions, according to fire officials. Firefighters searched every apartment to make sure that all the occupants were out of the building, said Kerrigan.There were no injuries reported, and the estimated 50 to 75 people who were evacuated were permitted back into their residences by Wednesday afternoon.

"It was mostly a smoke issue," he said, explaining the only occupant who will be temporarily displaced is the male resident of apartment 635.