SPRINGFIELD, Mass. » Building inspectors assessing homes and businesses in western Massachusetts’ largest city after a natural gas explosion says the blast damaged more than 40 buildings.

The Friday evening explosion in Springfield leveled a strip club next to a day care. It injured 18 people, many of them emergency workers. Their injuries aren’t life-threatening.

The explosion occurred an hour after gas company workers arrived to investigate a possible gas leak in the area that’s 90 miles west of Boston.

Authorities cordoned off the center of the explosion today. Building inspectors say preliminary findings showed the blast damaged 42 buildings housing 115 residential units. Three buildings were immediately condemned.

“It really is a miracle and it’s an example of our public safety officials, each and every day, putting themselves in harm’s way, taking what could have been considered a very routine call of an odor of gas, but they took the proper precautions,” State Fire Marshal Stephen Coan said. “And thanks to God that they did.”

Officials also marveled how the 5:30 p.m. blast occurred when a day care center next door was closed. The center’s building was heavily damaged.

“This is a miracle on Worthington Street that no one was killed,” Lt. Gov. Tim Murray said at a news conference. Murray and Springfield Mayor Domenic Sarno were attending a tree-lighting ceremony when the explosion occurred. Sarno said some people mistakenly thought the boom was part of the holiday event.

The explosion blew out windows in a three-block radius, leaving at least three buildings irreparably damaged and causing emergency workers to evacuate a six-story apartment building that was buckling, police said. Pieces of broken glass littered streets and sidewalks. It was unclear how many residents had been evacuated. A shelter was set up at a school.

Coan said his office has begun an investigation into the cause of the blast, as well as the possible origin. The state’s Department of Public Utilities was also investigating.

Sheila Doiron, a spokeswoman for Columbia Gas of Massachusetts, said the company will continue to monitor for any potential leaks within several blocks of the blast site. She said the company had already scanned the area and had not yet found any measurable readings.

Doiron said the company scanned its records and did not find any gas odor calls to the area where the strip club was located. She said the company does not yet know the source of the leak.

The victims were taken to two hospitals in the city. None of their injuries was considered life-threatening, officials said. Those injured were nine firefighters, two police officers, four Columbia Gas workers, two civilians and another city employee.

Springfield, which is 90 miles west of Boston and has about 150,000 residents, is the largest city in western Massachusetts. It’s known as the home of the Basketball Hall of Fame, which is not in the vicinity of the blast.

The city has been rebuilding from damage it sustained in a June 2011 tornado.

On Friday night, residents milled around the neighborhood where the explosion occurred, stunned by the destruction and confused by the cordoned-off area, which grew as crews continued to search for gas leaks. The mayor warned against looting, saying police would be out in force.

Wayne Davis, who lives about a block away from the destroyed building, said he felt his apartment shake.

“I was laying down in bed, and I started feeling the building shaking and creaking,” he said.

The Navy veteran said the boom from the explosion was louder than anything he’d ever heard, including the sound of a jet landing on an aircraft carrier.

The blast was so loud it was heard in several neighboring communities. Video from WWLP-TV showed the moment of the explosion, with smoke billowing into the air above the neighborhood.