WATERTOWN (CBS) – Four businesses on one block were gutted by a three-alarm fire in Watertown late Tuesday night.

The flames broke out in a commercial building on Main Street. A passing truck driver spotted the fire and called 911.

It took firefighters more than two hours to put the fire out.

The roof collapsed after an explosion that sent one firefighter to the hospital with a shoulder injury.

The building housed a barber shop and insurance company offices.

There’s no word yet on the cause of the fire.

Damage is estimated in the hundreds of thousands of dollars.