Police are now at the scene of the crash, which happened at about 5.30am today (Thursday), in Bingley Road at the junction with Toller Lane.
The road is now closed.
A spokesman for West Yorkshire Police said the closure was likely to remain in place "throughout most of the day".
Four people were seriously injured in the collision.
The incident has been referred to the Independent Office for Police Conduct, the police watchdog that investigates complaints against forces, the spokesman added.