Winnipeg police say a marijuana grow-op was found at this home on William Avenue after a fire broke out Saturday. (CBC)

Weekend fires broke out in two Winnipeg homes that were concealing marijuana-growing operations, police say.

An explosion at a William Avenue West home Saturday brought police and emergency crews to the Weston area at about 4:30 p.m.

There, a 29-year-old man was found suffering from second-degree burns. He was rushed to hospital in unstable condition for treatment, and remained there Sunday.

Neighbours said they heard a loud bang just before the fire broke out. Smoke poured out of the home's attic vents soon after, John Bailey said.

"The flames were like six feet [high], shooting out of the windows," Bailey said.

Police said 710 marijuana plants worth about $800,000 were found, along with about $20,000 in equipment used in growing them. No charges have been laid, police said.

Three hours later, another fire broke out around 7:30 p.m. at a suspected grow-op in the 700 block of Clifton Street. A 50-year-old man inside the home was treated in hospital for smoke inhalation.

Police said a "large quantity" of marijuana plants were found in the home, but didn't disclose exactly how many.

No charges were announced.

Damages at the William Avenue fire were estimated at $150,000. The Clifton Street home suffered $200,000 in damage, fire officials said. The cause of each fire remains under investigation.