Watch: Aerial footage shows aftermath of train crash in Sydney which left several people trapped and injured

Three people are trapped and several others are injured after a train hit a rail buffer at Richmond Station on Sydney's northwestern outskirts, with witnesses describing the scene as "chaotic".

Emergency services received a call just before 10am (local time) today with reports of injuries.

Local train at Sydney Central Station - Australia, New South Wales
Train at Sydney Central Station, Australia (file picture). Source:

Three choppers and 20 ambulance crews are attending, said NSW Ambulance.

Initial reports suggest 10 people are being treated for minor injuries, with two more severely hurt.

Three people are believed to be trapped in the front carriage, a NSW Fire and Rescue spokeswoman told AAP.

Paramedics were setting up a triage for patients.

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

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.