SPRINGFIELD, Mass.– Authorities in western Massachusetts have resumed an investigation of a natural gas explosion that damaged 42 buildings and injured 18 people.

Investigators and cleanup crews on Sunday returned to the blast area in Springfield, one of New England's biggest cities. The cause of the blast is under investigation. Police say the mayor will meet with investigators Sunday.

Friday night's explosion flattened a strip club and heavily damaged a day care center. It happened after officials evacuated part of the entertainment district because of reports of a gas leak and odor.