East Boston residents began returning to their homes late Friday, several hours after a 9-alarm fire consumed the headquarters of the New England Casket Company.

The fire was first reported around 3 p.m., with fire officials believing it began near a furnace used to dry wood for the business, according to reports.

"There was a sprinkler system, but the fire was above the sprinkler system," Boston Fire Department Commissioner Joseph Finn told Boston's WCVB-TV. "Our initial problems and why we are still here is the water supply, and this is because it just happens to be the end of the water supply for East Boston."

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Fire officials said as many as 100 firefighters from Boston and neighboring Chelsea attacked the blaze from multiple angles. The bulk of the fire was knocked down by around 10:30 p.m., they said.

"This is the biggest fire, for me, that I've seen as the mayor of this city," Mayor Marty Walsh told the station. "I'm just grateful that no one's hurt."

"This is the biggest fire, for me, that I've seen as the mayor of this city. I'm just grateful that no one's hurt." — Marty Walsh, mayor of Boston

However, two police officers who were working in the area were hospitalized for smoke inhalation, while two Boston firefighters were taken for exhaustion and one Chelsea firefighter was transported with a leg injury, according to WCVB.

All of the employees who were working inside the casket factory evacuated safely, Finn said, but the business is a total loss.

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Some area residents were evacuated to a nearby school because of the heavy smoke.

The regional transit system also reported that the Blue Line subway was suspended between the Orient Heights and Wonderland stops with shuttle buses replacing train service.

The Associated Press contributed to this report.