Two vehicles have crashed on the Sydney Harbour Bridge, causing delays and heavy traffic conditions. The white cars were involved in a head-on collision, with dozens of emergency service personnel on the scene assisting the drivers. NSW Ambulance confirmed two people were being assessed, with one of the two being put on a stretcher by paramedics. Traffic is slowly moving northbound with southbound traffic slightly more congested. Two out of three southbound lanes are closed, and one lane heading northbound is also blocked. Motorists have been advised to allow plenty of extra travel time and to exercise caution. Buses travelling over the bridge are warned to expect delays too.