The Patullo Bridge between Surrey and New Westminster, B.C., was closed in both directions for several hours Saturday afternoon after two vehicles were involved in a serious collision.

King George Highway approach to Pattullo Bridge

Traffic along King George Highway heading to the Pattullo Bridge is shown at a standstill just after 2 p.m. PT, about an hour after a serious accident shut down the bridge. (DriveBC)

Police say a southbound driver suffered a medical emergency and collided into a northbound vehicle sometime around 1 p.m. PT

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 estimated the bridge would be closed for four to six hours while investigators documented the scene and cleanup was completed. The bridge was re-opened at around 5:30 p.m.

Pattullo Bridge fight heats up between Surrey and New West

The Pattullo Bridge, which connects Surrey and New Westminster across the Fraser River, has been the scene of many head-on collisions. (CBC)

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.

With files from the CBC's Chad Pawson and The Canadian Pres