New London — Odor from a burst sewer pipe caused an hour-long evacuation of City Hall late this morning.

Mayor Daryl Justin Finizio said the incident was reported at 11:15 a.m.

Finizio said initially it was not certain what was causing the odor, which sickened four employees. He said the concern was that the odor was caused by gas or carbon monoxide.

He said the building was evacuated and emergency personnel responded to City Hall within five minutes of being reported. He added that firefighters determined that there was no gas meter readings in the building. The HazMat team from the Naval Submarine Base also responded.

The Ledge Light Health District, the city fire marshal and the head of the Department of Public Works have all cleared the building.

Employees were allowed back inside the building within five minutes. The employees who complained of feeling ill also returned to work.

Finizio said crews were working to find the source of the leak and cap it off.

Editor's note: This corrects an earlier version of this story.