WISCASSET — Firefighters are still investigating the cause of a blaze at a business on Chewonki Neck Road. The fire, which erupted late Sunday afternoon, took crews nearly five hours to knock down.

Wiscasset Fire Department Lt. T.J. Merry said he was the first on scene at Twin City Lock and Key shortly after 4 p.m. Sunday. When Merry arrived, a fire at the 4,000- square- foot metal- framed building was “fully involved.”

“The garage door in front had failed and heavy smoke and fire was coming out of that,” Merry said.

Workers who had been inside the building when the fire began evacuated safely, Merry said.

Before the blaze, Merry said, employees were “doing some welding on a vehicle and we’re thinking that might be the origin, but we’re still looking into that.”

Firefighters returned to the scene for about 30 minutes this morning to douse remaining hot spots in the metal building that Merry said posed challenges for fire- fighters on Sunday.

“With steel siding, it was difficult to gain access,” Merry said. “It was a strenuous fight.”

Merry said crews had to cut holes into the sides of the building with saws to attack the fire.

Because flames, heat and smoke were extensive when the first engine arrived, Merry said, crews set up a defensive attack.

“We were not going to put anyone in the building,” Merry said.

As of this morning, Merry could not provide a cost estimate for damage to the building at 137 Chewonki Neck Road.

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