BOSTON (AP) — A chimney collapsed in a four-story townhouse under construction in Boston's Back Bay, but officials say four workers inside at the time walked out OK.

A spokesman for the Boston Fire Department says the chimney collapsed Monday morning. Neighbors say they heard a huge bang and felt shaking.

Photos from the scene show a gaping hole left in the roof. Two nearby townhomes were initially evacuated as a precaution, but a building inspector says they are safe and people are allowed back inside.

A building inspector says the building is now secure.

A vacant residential building under construction in East Boston partially collapsed Sunday afternoon and was demolished Monday morning.

It was not yet clear what caused either collapse. Investigators are looking at whether the proper permits were issued.