A gas leak forced Wareham firefighters to shut down large sections of Main Street and Merchants Way Saturday afternoon, according to the Wareham Fire Department.

Asst. Chief Patrick Haskell of the Wareham Fire Department said the building at 219 Main Street had to be evacuated, after receiving a walk-in report of a gas smell at the back of the building, on the Merchants Way side.

“[The walk-in] said they had been smelling it for a couple days,” Haskell said.

Haskell said the responding firefighters could not find any evidence of gas outside the building, but, once inside, found evidence of a leak in the basement. After bringing in National Grid, the gas company that serves Main Street, it was discovered that the leak was coming from a pipe coming in from the street.

Several National Grid workmen on site said the leak “wasn’t a big deal,” but Haskell said otherwise.

“It was pretty serious,” Haskell said. “To them, it probably wasn’t that bad, but … if it had gotten to a point where the [gas] saturation [of the basement] got to a flammable level, it could have potentially [exploded]. But we hadn’t gotten there yet … we were over halfway.”

Haskell said there were three Wareham engines and two Onset Fire Department engines were at the scene, as well as two fire chiefs. Wareham Police dealt with traffic direction.

Haskell said gas ventilated out, once it was shut off, and that he believed National Grid was only going to deal with the pipe coming in from the street.

National Grid could not immediately be reached for comment.