Police are investigating whether a driver was highly intoxicated at the time he sped off from police and crashed into a power pole, leaving three women dead in western Sydney.

John Diing​ was driving a white Holden Commodore without his lights on when police tried to pull him over for a random breath test in the early hours of Saturday, police said.

After a pursuit lasting only a few seconds, the car careered off the road, crashed into a power pole and flipped onto its roof in Marayong.

Two women died on Railway Road, and another died in hospital.

"Police will be investigating all factors around the collision, including whether alcohol may have been a factor," Assistant Commissioner John Hartley said on Sunday.

Friends said the women who died had 12 children between them.

Roza Mawen was a Sydney mother of four, while Bianca Goak​, from Melbourne was a mother of eight.

Adut Garang​ also died as a result of the impact.

The driver, Mr Diing, was still at Westmead Hospital in a stable condition on Sunday night.

Police said he had undergone blood and urine testing.

The only surviving passenger was Asunta Jongkor​, a mother of 10, who was in a stable condition on Saturday.

Her husband, Arkangelo Kon, said his wife had explained the group had been at the house of Ms Mawen and were travelling to another house at the time of the crash.

He said she had no memory of the car crash but was in a "bad condition" when she learnt her three friends had died.

"It was a terrible time … but I thank God that she is still alive," Mr Kon said.

Tresa Diing, a South Sudanese community leader and the aunt of Mr Diing said everyone on the car was related and had come to Australia from their war-torn country for a better life for their children.

She said she wished her nephew had stopped when the police tried to pull him over.

"If you drive away from police you are breaking the law," she said.

"If they had stopped we wouldn't be in such tragedy. The police were doing their job, we cannot blame the police."

with Matt O'Sullivan