A man is in a serious condition in hospital after his car burst into flames before it rammed the roller door of the Merrylands police station car park in Sydney's west.

Police said it was a "miracle" no police or bystanders were injured in the incident.

The ABC understands the car had two gas bottle inside and the man, who is stable in Royal North Shore hospital with burns, claimed he had a bomb.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 3 seconds 1 m 3 s The car rammed into the police station's roller door

NSW Police Assistant Commissioner Denis Clifford said police officers spotted a man parked in the driveway of the police station about 7:00pm.

"As police approached the vehicle, the interior of the vehicle ignited," Assistant Commissioner Clifford said.

"The man then drove that vehicle down the driveway and collided with the roller shutter door, underneath the police station.

"The vehicle collided heavily with the roller shutter, that stopped the vehicle.

"He was unconscious for some time, police extinguished the flames and extricated the person from the vehicle.

"It happened very quickly, the officer approached the vehicle ... that's when he, possibly, ignited some sort of accelerant in the car and then drove down the driveway to the roller shutter door."

Bomb disposal experts have been called in to examine the car. ( ABC News: Raveen Hunjan )

Assistant Commissioner Clifford said police were still trying to establish the man's identity, but it appeared that the man was working on his own.

"He has been treated by ambulance and taken to hospital in a serious condition, with what I understand are very serious burns," he said.

"We don't know what the motivations are at this stage, we're still trying to work through all of that.

"There's nothing to indicate that this is in any way related to terrorism.

"We'll keep an open mind, but we're not leaning towards that at this stage."

The ABC understands the man is aged in his 60s, was known to police and may have mental health issues.

Assistant Commissioner Denis Clifford says investigations are continuing into the incident. ( ABC News: Jess Kidd )

Assistant Commissioner Clifford praised the "very, very brave" officers who responded.

"They've approached the vehicle, I understand the vehicle had an amount of accelerant, fuel in the vehicle and they've approached to save this person's life.

"The police are on high alert and we've been that way for some time, due to events here and overseas."

The incident occurred in a busy residential and shopping precinct and Assistant Commissioner Clifford said he had no doubt that locals were concerned.

He asked anyone who witnessed or had footage of the incident to come forward.

"It's very concerning, this is a serious incident, the police reacted very bravely and it's just a miracle no-one else was seriously injured."

He said investigations were continuing and did not confirm what sort of accelerant was in the car, but said it was some kind of fuel and the Rescue and Bomb Disposal Unit was examining the vehicle and making sure it was secure and there was no further threat.

Police have removed two gas cylinders from the car.

A police statement said initial inquiries suggest the man did not links to specific groups.

Memorial Avenue was closed to traffic and Fire and Rescue crews were at the scene.