Monday afternoon’s blast at the New Hampshire Ball Bearings Inc. plant in Peterborough is being investigated but all indications were that it was an industrial-related incident, said Peterborough Fire Department spokesman Eric Bowman. There didn’t appear to be any environmental damage.

Plant machine operator Paul Clark said he was outside in the parking lot when he heard the explosion.

“I was in my car backing out when I felt a rumble and heard a bang,” he said. “I looked up, and snow on the building’s roof was flying into the wind.”

The plant, in the southwest New Hampshire town that was the inspiration for Thornton Wilder’s play “Our Town,” manufactures high-tech parts for the aerospace industry and employs 700 people. Company spokeswoman Kathy Gerrity said she wasn’t sure how many people were inside when the explosion happened but there are usually about 450 working around that time.

The blast blew out windows on the three-story building’s ground floor, and the first arriving firefighters saw a column of smoke, said Bowman.

Clark, who operates a machine used in a rolling procedure, said his girlfriend, Andrea Painchaud, was at work in the shipping department when the explosion knocked shelves off the walls and part of the roof came down around her. He said she was uninjured.

“Smoke came pouring out,” said Clark, who lives in nearby Pepperell, Mass. “I could hear somebody screaming.”

Bill Brock, owner of the Manhattan East Hair Design shop about a quarter-mile from the plant, said he heard and felt something but didn’t know what it was. Then about 30 ambulances and fire trucks went by.

Gov. Maggie Hassan said the state emergency operations center was open to monitor the situation and she was “very encouraged” to hear that all employees had been accounted for.

“My thoughts and prayers go out to those injured in today’s explosion, to their families and loved ones, and to the entire Peterborough area where NH Ball Bearings is such an important member of the community,” she said in a statement.

Two of the 15 people injured were treated at Monadnock Community Hospital and later were flown to other hospitals, spokeswoman Laura Gingras said. The rest were released by Monday night.

Bowman said in a news release that two people had suffered critical injuries.

Peterborough has about 6,400 residents. Besides inspiring “Our Town,” a Pulitzer Prize-winning play first performed in 1938, it is home to the MacDowell Colony, a prestigious retreat for artists, writers and composers. Wilder based the fictional town of Grover’s Corners on Peterborough, where he often spent his summers.

New Hampshire Ball Bearings’ corporate headquarters are in Chatsworth, Calif. It’s a division of Japanese company Minebea.