A fire at a greenhouse facility that produces medical marijuana kept St. Catharines firefighters busy early Wednesday.

The fire destroyed a barn, but firefighters saved the attached greenhouse and its contents, Deputy Chief Dave Upper said.

The call about a working fire at 376 Read Rd. on the east side of the Welland Canal came in at 1 a.m.

"When the crews arrived, they were presented with a significantly large fire," Upper said. "They immediately set up defensive operations, and crews worked through the night to get the fire under control."

Fire prevention officers were at the scene later in the day working on damage estimates. The Office of the Fire Marshal was notified, but won't be attending.

The fire department confirmed with Health Canada the greenhouse is a legal, medicinal cannabis operation, Upper said.

"The plants in the greenhouse were fine with minimal damage," Upper said. "The fire was mostly in the barn which serves as a storage and processing area."

Later in the day, the fire department called in an excavator to pull the barn apart and help fire prevention officers with their investigation. Upper said the excavator was also used to search for leftover hot spots.

Unlike some recent greenhouse fires, for which firefighters relied on a relay of tanker trucks, water supply wasn't an issue. There was a hydrant on the adjacent property, Upper said.