HARTFORD, Conn. – Part of a bridge under construction in Naugatuck collapsed early Tuesday, injuring a worker who had just warned colleagues to get off the span because he was worried about its stability.

Anthony Mariano, 59, of Middlebury was operating a piece of heavy equipment, and was hospitalized after the incident on the Route 63 bridge over the Naugatuck River, police said. That span, also known as the Salem Bridge, is being replaced as part of a $24.5 million state project.

He was taken to Waterbury Hospital in critical condition, then transferred by helicopter to Yale-New Haven Hospital.

The affected section of the bridge was closed to traffic at the time of the collapse, and no motorists were hurt.

About 100 feet of the 586-foot bridge buckled and fell as construction crews used a pneumatic jackhammer mounted on an excavator around 6:30 a.m. to break up concrete on the bridge decking, authorities said.

Marinano, who was operating the excavator, had just told his supervisor he was concerned about the bridge’s stability and had warned other workers to leave. He was moving the equipment off the bridge when it collapsed, police said.

He works for Southington-based Brunalli Construction, a large construction contractor with five other bridge repair and replacement projects under way in Connecticut. A woman who answered the phone at Brunalli’s offices Tuesday said the company had no comment.