Waterbury firefighters continue to battle a massive fire in an abandoned factory building at the intersection of South Main Street and Pearl Lake Road that started Saturday night, and now officials believe the fire was deliberately set.

The fire broke out inside an old factory building around 8:45 p.m. Saturday according to the fire chief. There were no reports of injuries to firefighters or civilians, he said.

Authorities say the factory used to be a manufacturing mill that has sat abandoned for several years. Officials estimate that the building has been abandoned for 10 to 15 years.

Firefighters were able to bring the fire under control before midnight, but planned on staying through the morning to continue putting out hot spots.

Flame embers carried by the wind damaged an adjacent building, but the extent of the damage was not known, the fire chief said.

As of Monday morning, the fire was still smoldering. Fire crews will use heavy machinery to break up the rubble and get to voids where the fire is currently out of reach. Fire officials said the fire appears suspicious.

"We have an empty building, no electricity, a great volume of fire moving through the building quickly. It's all the indication it had help," said Waterbury Fire Chief David Martin.

The cause of the fire remains under investigation.