GORHAM — An electrical fire that was started by a bathroom fan Thursday night burned through the upper floors of the building that’s home to the Gorham House of Pizza, shutting down the popular restaurant and drawing a state investigator to the town that has been hit by six suspicious fires since late March.

Danny Young, senior investigator for the state Fire Marshal’s Office, said Friday that the fire was accidental and not related to the string of arsons at vacant buildings in the northern part of Gorham.

The fire started about 9:30 p.m. in an apartment on the second floor of the three-story building at 2 State St., in the town center at the intersection of routes 25 and 114. The building is owned by Angelo Sotiropoulos, who opened the Gorham House of Pizza on the first floor 31 years ago.

Six tenants, four of whom are students at the nearby University of Southern Maine, were displaced from the two apartments on the upper floors. No one was injured.

Although the restaurant wasn’t damaged by fire, it sustained extensive water damage as firefighters doused the blaze and it probably won’t reopen for at least a few months, Young said.

Amanda Hayes, who was working at the restaurant when the fire started, said she and other employees smelled something burning and first thought it was food in the kitchen. A tenant from one of the apartments came into the restaurant to say there was a fire upstairs, she said.

Firefighters from eight departments responded.

Young and others who are investigating the arsons in Gorham have been working late nights since the first of six suspicious fires was set on March 27. Thursday was the first night they were sent home early to get rest, he said.

Then, the call came in for a fire in Gorham.

Young said he went to the scene to make sure the fire wasn’t related to the arsons, then completed his investigation Friday morning, after the fire was extinguished.

Hayes, who has worked at the restaurant for 10 years, since she was 16, said, “It was like watching my house burn down.”

Hundreds of people gathered at the scene of the fire, offering comfort to Sotiropoulos and watching firefighters battle the blaze into the night, said Fotine Sotiropoulos, the owner’s daughter. She said she never thought the fire was arson.

The fire was extinguished between 2 and 3 a.m. Friday, Young said. It was the second accidental fire in town since the arsons began.

Steve McCausland, spokesman for the Department of Public Safety, said Friday that the investigation into the arsons continues and investigators are still encouraging residents to report any suspicious activity.

“It takes only one good observation from a resident or passer-by to bring this string of arsons to an end,” he said.

Sotiropoulos, 62, who emigrated from Greece nearly 40 years ago, said he was devastated Thursday night, but the support from the community “kept me going.”

Customers and friends of his, who stopped by the restaurant Friday morning, said the owner’s cheerfulness and sense of humor have made the restaurant such a popular place.

“He’s Gorham’s icon,” said Jeff Murphy of Windham, a customer.

Sotiropoulos, who lived above the restaurant for 13 years before moving to another home in Gorham, said he was grateful that no one was hurt and that the building wasn’t destroyed.

“It stands. There’s damage, but it stands,” he said.

USM and students at the university moved quickly Friday to help the four who lost their living quarters to the fire.

The university said it moved the students into on-campus housing, the Aramark food service donated meal plans and the USM bookstore offered to loan the students replacement textbooks.