LEWISTON — Fire crews doused an early morning fire at a medical marijuana grow facility Tuesday and investigators say spontaneous combustion is the likely cause.

The blaze at The Gas Station, a cannabis dispensary at 1822 Lisbon St., burned through a grow room and filled the building with black smoke, fire officials said.

The fire was reported at about 6:45 a.m. After firefighters knocked down the flames, an investigation got underway. Fire inspector Paul Ouellette said later that most likely, the cause was spontaneous combustion in potting soil.

“They use coco husk potting soil, that can spontaneously catch fire,” Ouellette said. “This can and has happened to other potting soils that even homeowners have.”

Ouellette said similar fires have been reported all over the country, including at least one that occurred in northern Maine a few weeks ago.

Fire officials have warned that the potting soil, which contains organic dry matter such as coco coir, peat moss and bark, can burn under both extreme natural circumstances or human negligence.

The lighter the organic material used in the potting soil the higher the chances of it catching fire, officials cautioned. The potting mixture decomposes over time, which produces bacteria and under certain conditions, it can generate heat and spontaneously combust into a fire.

Ouellette said it was too soon to say how much damage was caused at The Gas Station in the blaze. The fire was confined to one grow room out of seven at the business.

The Gas Station has three stores in Maine.