Three people were transported to hospital and one of them remains in critical condition after a TTC bus collided with another vehicle in Scarborough on Christmas Eve.

The collision happened at around 5:30 p.m. on Sheppard Avenue East. According to police, it started off near Meadowvale Road and ended about seven kilometres away at Havenview Road, west of Markham Road.

Police said the 58-year-old driver of a sedan appears to have suffered a medical episode and collided with two other vehicles before finally slamming head-on into the TTC bus.

Toronto Paramedic Services said the driver, the lone occupant of his vehicle, was taken to a trauma centre with serious injuries. However police later said his injuries are considered life-threatening.

Two people from the other vehicles were taken to hospital with minor injuries, police said.

Images from the scene showed the small sedan with extensive front-end damage, still lodged in the front of the bus.

All of the vehicles sustained significant damage, police said.

The westbound lanes of Sheppard Avenue are currently closed between Markham and Havenview roads as police investigate the collision.

The incident comes just a day after another TTC bus was involved in a collision on Parkside Drive in the Roncesvalles area, leaving one person, seriously injured.