NORWALK, Conn. (AP) — Two Connecticut firefighters needed medical treatment after helping to put out an early-morning blaze.

Authorities say one firefighter was treated for a knee injury and the other suffered dehydration after fighting the fire at a store on Main Street in Norwalk early Thursday. Nearly 40 fire officials worked to put out the blaze.

High amounts of carbon monoxide were found in apartments above the store, prompted officials to evacuate them. The cause of the fire is under investigation.