Police are today appealing for information following after the collision at around 12.40pm on Monday, September 4 on Milton Avenue, Sowerby Bridge
A multi-coloured Optare Solo bus was travelling in the direction of Albert Road when it collided with a stationary Ford Transit van.
The impact caused the bus to cross to the other side of the road where it collided with a tree. The bus then collided with a parked Landrover Discovery vehicle.
A passenger on the bus, a woman in her 80s, received treatment for minor injuries at the time. Her condition has since deteriorated and she is now in hospital in a serious condition.
Anyone who witnessed the collision or anyone who saw the bus driving in the area beforehand is asked to contact the Safer Roads team.
Information can be passed on by calling 101, quoting log number 720 of September 4.