It happened at about 8.45am today (Saturday).
A 91-year-old man was hit by a car as it turned right at the junction from Market Street to Chapel Lane.
He was taken to hospital with serious injuries.
Police have closed the junction as they investigation the incident.
A spokesperson for West Yorkshire Police said: "At 8.52am police were called to reports of a serious road traffic collision in Birstall.
"The incident occurred when a vehicle turning right at the junction from Market Street to Chapel Lane was in collision with a pedestrian.
"The pedestrian, a 91-year-old male has been taken hospital with serious injuries.
"A scene remains in place as enquiries remain ongoing."