State highway personnel are assessing damage to the Tip O’Neill tunnel after a truck struck the tunnel’s ceiling.

The truck, which was being carried on a flatbed by a tractor, hit the ceiling of the tunnel on Route 93 southbound at 9:40 a.m. and has caused “potential damage to wires and light fixtures,” according to a Massachusetts State Police alert.

The damaged wires have been removed and the truck has exited the tunnel and is in the breakdown lane of Route 93 southbound, according to an alert.

Traffic is backed up to the Zakim Bridge, and all lanes have reopened, the alert says.