A rolled-over tractor-trailer has spilled 23,000 litres of fuel near a conservation area in Caledon — and it's still leaking into nearby ditches.

The truck's pup trailer rolled over overnight on Highway 9, near Airport Road and the Glen Haffy Conservation area.

Hwy 9 blocked near Airport Rd for fuel tanker spill. Crews worried fuel leaking into nearby creek & conservation area <a href="https://t.co/H604zLFfpj">pic.twitter.com/H604zLFfpj</a> —@LindaWardCBC

OPP Const. Stephanie Hammond said the fuel spill so far has been significant and up to 33,000 litres could spill if the leak isn't stopped soon.

"It's gone into the ditches, it's gone into the catch basin. But the catch basin does not flow into the Humber River itself," she said.

A stretch of Highway 9 near the spill is currently closed, and will likely stay that way until 3 or 4 p.m. as emergency crews — including firefighters from Caledon and Brampton, Halton Spill Control, the Ministry of the Environment and Ontario Provincial Police — remain on scene for spill control.

Police have closed a portion of Hwy. 9 near Airport Road after a rolled-over tractor-trailer spilled 23,000 litres. 0:22

Crews trying to prevent wetland contamination

"This'll be a big effort here to get this cleaned up," Hammond said from the scene, adding rain is complicating the situation.

Caledon Mayor Allan Thompson said three basins have been set up in the ditch to catch fuel. But the spill is proving tricky to contain.

"​The back trailer is what they're trying to deal with at this point," he said. "The puncture can't be contained... so they're pumping off (fuel)."

The main focus right now "is to prevent contamination of the wetland," Thompson added.

The fuel spill is in a sensitive area just north of Glen Haffy Conservation Area. (Tony Smyth/CBC)

It's not clear why the driver lost control, said Hammond, but "speed doesn't seem to be a factor at this point."

No injuries have been reported.