Springfield, Mass. — Preliminary inspections show that more than 40 buildings were damaged in one of New England's biggest cities Friday when a natural gas leak led to an explosion that injured 18, building inspectors said Saturday.

A strip club was flattened and a day care center was heavily damaged in the massive blast. No one was killed.

Investigators Saturday were trying to determine what caused the blast that was heard for miles, left a large hole in the ground where the multistory brick building housing Scores Gentleman's Club once stood, and scattered debris over several blocks.

After responding to an odor of gas reported about an hour before the explosion, officials evacuated part of the entertainment district. Gas workers venting the leak saw indications that the building was about to explode and, along with firefighters and police officers, ducked for cover behind a utility truck just before the blast, said Mark McDonald, president of the New England Gas Workers Association.

Most of the injured were in that group, and the truck that saved their lives essentially was demolished, he said.

"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 at how the 5:30 p.m. blast occurred when the day care center next door was closed. The center's building was heavily damaged.

Lt. Gov. Tim Murray and Springfield Mayor Domenic Sarno were attending a tree-lighting ceremony when the explosion occurred. Sarno said some spectators mistakenly thought the boom was part of the holiday event.

The blast shattered windows over a three-block radius, left at least three buildings irreparably damaged and prompted 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 Saturday how many residents had been evacuated. A shelter was set up at a school, but city officials said no one stayed there overnight.

Omar Fermin, manager of the Punta Cana Restaurant two blocks from the explosion site, found the floor-to-ceiling windows blown out when he came to check on the property Saturday morning.

"It looks like an earthquake hit," the Dominican Republic native said. "I've never seen anything like it."

As Fermin waited for someone to come and assess the damage, he worried the restaurant would remain closed for weeks while the owner sought to replace the massive, custom-made windows.

Authorities cordoned off the explosion area Saturday as building inspectors worked to identify unsafe structures. Anxious residents gathered at the perimeter, waiting for permission to visit their buildings.

Preliminary reports show the blast damaged 42 buildings comprising 115 residential units, and police officers were deployed throughout the area to prevent looting, said Thomas Walsh, spokesman for the mayor.

Three buildings were condemned immediately, and 24 others would require additional inspections by structural engineers to determine whether they are safe, Walsh said.

Dogs trapped in abandoned buildings barked loudly Saturday as inspectors fanned out across the area. One inspector said he wished he could get a ladder and permission to retrieve a dog that was barking on the upper floor of one building that was sealed off from residents.

Authorities are opening an animal shelter for pets affected by the explosion, Walsh said.

Coan, the fire marshal, said his office is investigating the cause of the blast and its origin. The state's Department of Public Utilities also was investigating.

Sheila Doiron, a spokeswoman for Columbia Gas of Massachusetts, said the company will continue to monitor for leaks within several blocks of the blast site. So far, she said, the company hadn't yet found any measurable readings.

The utility will keep at least 30 workers at the scene, along with a so-called sniffing car mounted with sophisticated gadgets capable of detecting low level natural gas leaks, Walsh said.

The victims — nine firefighters, two police officers, four Columbia Gas workers, two civilians and another city employee — were taken to two hospitals in the city.

Springfield, which is 90 miles west of Boston and has about 150,000 residents, is the largest city in western Massachusetts. It's known for being home to the Basketball Hall of Fame, which is not near the blast site.

Associated Press writers Rodrique Ngowi, Bridget Murphy and Bob Salsberg in Boston and Jessica Hill in Springfield contributed to this report.