Around 16 people were injured when a train failed to brake and hit a barrier at Richmond Station in Sydney's north-west on Monday morning, with one witness saying passengers were sent "flying like Superman".

The passenger train was "slowing to stop at the station" when it crashed into a buffer at the end of the line, according to New South Wales Police.

Initial reports suggested the train derailed, but Sydney Trains CEO Howard Collins said it was still on its rails.

This man was treated for his injuries after the train crashed at Richmond Station. ( Facebook / AAP: Glenn Campbell )

Richmond Station was closed after the crash.

NSW Ambulance said around 16 people were injured, with all patients that were taken to hospital in a stable condition.

A 77-year-old woman is being treated for possible collar bone and spinal injuries and a 22-year-old man has a suspected broken femur.

A spokesperson for the Western Sydney Local Health District said all five patients transferred to Blacktown Hospital have been discharged.

Four patients remain in a stable condition at Westmead Hospital, while one person has been discharged.

NSW Police said no-one was trapped in the train during the incident.

Blood can be seen on the floor of a train at Richmond Station in Sydney's north-west. ( Facebook: Brett Saunders )

Conflicting reports over train speed

Mr Collins said it was "difficult" to say how fast the train was travelling when it hit the buffer.

Brett Saunders, who witnessed the crash just before 10:00am, described it as "horrifying".

"I was on [the] platform waiting for it to stop, but it did brake and crashed at full speed into the barrier sending everyone flying like Superman. It was insane," he said.

Witness Kimberley Sullivan was going through the nearby McDonald's drive-thru when she heard a loud bang.

People are treated at the Richmond and District Memorial Oval. ( ABC News: Mark Reddie )

"[We] saw that the train had hit the end … it looked like it really slammed its brakes on," she said.

"It wasn't going very fast, about five to 10 kilometres an hour.

"We saw the part that connects to the cables came off but then went back on again."

NSW Transport Minister Andrew Constance said there would be three independent investigations, run by different agencies, into the crash.

This woman was treated at the scene after the accident. ( AAP: Glenn Campbell )

'Train driver is OK'

The crash continues a diabolical month for Sydney Trains, whose network went into meltdown two weeks ago with widespread delays and station closures.

The NSW Government, Sydney Trains and the drivers' union are also locked in a pay dispute, with a strike planned for January 29.

Mr Collins described the crash as a "most unusual occurrence".

"My first thoughts are with those people who have suffered injury," he said.

Injured passengers are loaded off the train and onto stretchers. ( Supplied: Careflight )

"The train driver is OK, obviously serious shaken."

Mr Collins said the buffer stopper had done its job.

"The most important thing is to understand the facts, work with those people who are doing the investigation on site, and then we will be able to tell people why this incident occurred," he said.

"As far as I'm concerned, the railway is running well in other parts of the network."

The train involved was a new Waratah train but Mr Collins said nothing indicated the other Waratahs needed to be halted for now.

The front of the train was significantly damaged in the incident. ( Facebook: Brett Saunders )

Noel Keogh witnessed the incident and said some carriages "came up in the air like a pyramid" after the impact.

"I just ran because I thought it was going to come off the tracks," he said.

"The ground shook and everything."

Salary negotiations between Sydney Trains and the Rail, Tram and Bus Union over pay conditions were halted when news of this morning's crash reached the meeting.

Sydney Trains was reporting the Western Line had only a partial closure due to the crash, with buses replacing trains between Richmond and Clarendon in both directions.