Two people are in serious condition, including an Edmonton Transit System bus driver, following a collision involving an ETS bus, a semi truck and two other vehicles Saturday evening.

The crash happened near the intersection of 102nd Street and 111th Avenue at around 7 p.m.

Witnesses say a semi truck was making a left hand turn at the intersection.when it collided with an Edmonton transit bus.

"I thought something exploded," said nearby resident Kem Cheong Chau. 

Two other vehicles were also involved in the collision.  Edmonton Fire Rescue officials say four people were sent to hospital, with the bus driver and one other person being listed in serious condition.  

Brent Welch, a witness who was on scene moments after the crash, says the bus driver was trapped inside the bus and had to be removed by EMS and Fire Rescue personnel. 

"I could see the bus driver was trapped," said Welch.  "They had to extricate him from the bus.  He was unconscious too."

Welch says he heard the crash from his nearby apartment and called 911.  He says as a fellow ETS driver he was devastated to see the driver so badly hurt. 

"It was very disheartening to see him put on the stretcher and taken away once they got him out," said Welch. 

The bus driver who Welch describes as being middle-aged was taken to hospital where he is reportedly in serious condition. 

It is not known whether any charges will be laid.