New London — Renovations at one of the country's oldest continuously used courthouses sparked a fire Tuesday that forced evacuations of both wings of the building at 70 Huntington St.

No one was injured in the 1:57 p.m. blaze, which began accidentally when a contractor connecting the air conditioning system in the rear attic of the old Superior Court building sparked the fire, Battalion Chief Thomas Curcio of the New London Fire Department said.

The old wing of the courthouse has been undergoing renovations and appears close to completion. Both the old wing and the new wing of the courthouse have been in use.

The original portion of the building, a Georgian-style building topped with a cupola, opened in 1784. An addition was built two centuries later, in 1982.

The facade of the Huntington Street courthouse — the New London Judicial District courthouse — is being renovated during a yearlong $895,000 project. The plans called for the cleaning and re-pointing of the stone masonry foundations and brick walls, removal and replacement of clapboard siding, removal of rotted wood trim, repairs to the slate roof and repair and restorations of the decorative wood cornice and rake-and-eave trim.

The scene was cleared by late afternoon, and the intersection of State and Huntington streets was reopened.

Pete Willette, an employee of the Beaulieu Co., said he was installing copper gutters on the courthouse when the fire began. He said the air conditioning contractor was brazing a pipe during installation, sparking the blaze.

The company also recently finished the building's new slate roof, Willette said, a portion of which was "cooked" by the fire.

Fire Chief Ronald Samul said the contractor who accidentally started the fire tried to put it out but could not. The sprinkler system kicked in, Samul said, and suppressed the blaze sufficiently until the fire department responded.

"Everyone was evacuating when we got here," Curcio said.

Curcio said the fire was knocked down in about 15 minutes and declared out in about 35 minutes. Firefighters continued Tuesday afternoon to rip off siding to make sure the fire had not spread within the walls of the building, Curcio said.

The courthouse was closed for the rest of the day, and trials that were under way did not resume. Officials were concerned about residual smoke in the building, and alarms weren't working while fire crews worked.

Employees were allowed into the building to retrieve their belongings.

According to a judicial branch spokeswoman, damage to the old building has to be assessed, and it may be some time before it's available for use. In the newer section, there continued to be an odor of smoke Tuesday afternoon, and officials were assessing whether it would reopen Wednesday.

Curcio said his department called in mutual aid from Waterford for a second ladder truck. The submarine base FAST team also responded, he said.

s.goldstein@theday.com

k.florin@theday.com