The accident happened on the corner of Widemere and Davis roads in Wetherill Park about 9.40am on Tuesday.

The garbage truck travelling on Davis Road collided with a bus travelling on the Transitway, causing the bus to leave the road, cross a grass embankment and hit several parked cars in a car park, a NSW Police spokesman said.

The cause of the accident was the "truck going through a red light," a spokeswoman for Transit Systems buses said.

The Transit Systems bus, on the T80 route from Parramatta to Liverpool, was carrying 20 passengers.

The accident left the front of the bus completely shattered and mangled.

The driver was trapped for a short period of time and Fire and Rescue NSW crews had to cut the front door off to free him.

He was taken to hospital and "is naturally shaken but ok," the Transit Systems spokeswoman said.

Six of his passengers were also taken to hospital.

Another nine passengers were treated at the scene for various injuries including fractures and bruising.

"The male driver of the garbage truck was uninjured. He was breath tested at the scene and returned a negative result," a NSW Police statement said.

A spokeswoman for garbage truck company Remondis said the driver, aged in his 50s, had been with the company for more than 10 years. She said he was working at the time of the crash.

"He's in shock at the moment, he's very shaken to have seen people injured," she said. "He will be getting counselling later today."

She declined to comment on the cause of the crash.

A NSW Ambulance spokeswoman initially said nine patients were being treated at the scene with a range of injuries.

"We're treating nine patients [including] two with serious injuries and four with non life-threatening injuries," a NSW Ambulance spokeswoman said.

"The injuries range from cuts from broken glass to someone with a suspected broken arm."

More to come

/**/