The Patullo Bridge between Surrey and New Westminster, B.C. has been closed in both directions since approximately 1 p.m. PT after two vehicles appear to have been involved in a serious collision.
Police say a southbound driver suffered a medical emergency and collided into a northbound vehicle.
A photograph distributed on social media appears to show a taxi and a black sedan, both with significant damage, at the accident site.
Four people, two in each car, were transported to hospital. One person reportedly has serious injuries.
Police estimate the bridge would be closed for four to six hours while investigators document the scene and cleanup is completed.
The bridge, which has four narrow lanes and a curve on one approach, has a recent history of many serious and deadly collisions, most of them head-on.
Nighttime closures of one lane in each direction were introduced almost a decade ago as a safety measure.