An elderly woman and several others have been injured after a train hit a railway buffer at Richmond Station on Sydney's northwestern outskirts, with witnesses describing the scene as "chaotic".

Emergency services were called to the station just before 10am on Monday.

Three choppers and 17 ambulance crews are attending, NSW Ambulance said.

Two people have suspected spinal injuries, while another has a possible broken collarbone and another a broken leg.

A 70-year-old woman has been taken to Westmead Hospital for treatment and two others have been transported to Nepean.

Passengers trapped inside a train at Richmond Station after the carriage overshot a platform and struck a barricade. #9News https://t.co/teDcQNcewt pic.twitter.com/FnLJJjrCRm

— Nine News Sydney (@9NewsSyd) January 21, 2018

Witnesses have described a scene of chaos, with the train apparently hitting the buffer at the end of the line "at speed".

One caller to Sydney's 2GB radio who saw the crash said there was an "almighty bang".

He said the train came in at speed and hit the buffer and rebounded.

"There was a huge amount of dust," he said.

"It's all chaos here," another caller, Steve, told the station.

Transport for NSW said it was aware of the incident .

"No customers or staff are trapped," it tweeted.

"We are working with emergency services and NSW Ambulance is treating injuries. We will provide more information as it becomes available."