The Coquihalla highway is closed in both directions 500 metres south of Exit 286 as a result of a formaldehyde spill.
A tanker truck tipped over into a ditch, spilling its load into a drain. The driver is not injured.
RCMP are keeping people away from the scene because of the danger of inhaling fumes.
The formaldehyde is not affecting any waterways, and there is no environmental issue, but environmental consultants are on their way to the site, according to B.C.'s Ministry of Environment.
Drivers are told to take a detour via Coldwater Road, Exit 256, until further notice. The Ministry of Transportation says it does not know how long the closure will be in effect.
With files from The Canadian Press
