MANCHESTER, N.H. (AP) – A natural gas leak Thursday morning closed the city’s main street and prompted officials to evacuate several buildings, including City Hall.

Crews searched for hours for the source of the leak that reached potentially explosive levels. “It could have been catastrophic,” said District Fire Chief Mike Gamache. “Gas leaks have been known to take down blocks this size and more.”

A pedestrian smelled the gas at 8:30 a.m. and called the fire department. Police shut down several blocks of Elm Street between Merrimack and Amherst streets. The affected buildings included City Hall and the multistory Citizens Bank building.

Gamache said the type of leak that was detected could have been ignited by something as simple as someone walking along the sidewalk and striking a match.