PICKERING, Ont. -- A man is facing more than 300 weapons-related charges after firefighters responding to a carbon monoxide alarm at a home in a community east of Toronto found something suspicious.

Durham regional police say firefighters who went to the Pickering, Ont., home on Wednesday called police after spotting an unknown substance in the basement.

They say officers, aided by an Ontario Provincial Police clandestine lab team, located an unidentified substance along with 33 guns and other prohibited devices, such as overcapacity magazines.

Police spokeswoman Jodi MacLean says the owner of the home -- a 33-year-old man from neighbouring Oshawa, Ont., -- is facing 337 charges.

Those charges include careless storage of a firearm, unauthorized possession of a firearm and possession of a restricted or prohibited firearm.

MacLean says the substance found in the home has been sent for analysis.