Police said they were called to George Street just after 8am, following a report that a pedestrian had been hit by a bus.

Police have since confirmed that the accident involved two cars, and the drivers of both vehicles have been taken to hospital for mandatory blood and urine testing.

The pedestrian has been taken to St Vincent's Hospital in a critical condition, the NSW Ambulance Service said.

Police have reopened lanes in both directions on George Street.

The accident triggered heavy traffic congestion in the area, but this has since cleared.

Motorists were earlier being diverted into Bathurst Street, and the Transport Management Centre has advised motorists to allow additional travel time.

Buses in both directions along George Street have returned to their normal routes.

At 9.30am, emergency services were still working in the bus lane.

#Route422 #Route423 #Route426 #Route428 delayed up to 30 mins & diverting off George St via Elizabeth St in CBD due to pedestrian & car acc — Buses Info (@BusesInfo) March 5, 2015

Pedestrian taken to hospital after incident on George St, Syd CBD, believed to involve 2 cars. — NSW Police (@nswpolice) March 5, 2015

George St closed btw Bathurst and Liverpool Sts. Contra-flow in place on George St for buses only. — NSW Police (@nswpolice) March 5, 2015

Oh man. Nasty accident on George St. Paramedics doing their best. — Chris Hagen (@chris_hagen) March 5, 2015

Oh no - another pedestrian accident - Sydney CBD - George St sthbnd just past Bathurst St. Sthbnd is now closed at Bathurst St. — Paul Latter (@paullatter) March 5, 2015

A pedestrian died after he was hit by a car in Pyrmont on Thursday.