West Vancouver police say one lane northbound has been reopened following a rockslide north of Horseshoe Bay.
There were no reports of injuries.
Drivers heading up Highway 99 say the rockslide happened just after 3:30 p.m. PT.
John Vos was caught up in the traffic jam after the incident. He said the slide appeared to have taken down some power lines as well.
"The rock was probably about the size of a large vehicle," he said.
West Vancouver police say crews are on scene to trying to clear the road.
#WVPDTraffic - One lane reopening Hwy#99 NB- Removal of rockfall north of Ansell Place is ongoing.— @WestVanPolice