A 41-year-old woman has died after being violently attacked on her way home in Sydney's west.

A man passing by a laneway near Amos Street in Westmead found the woman lying on the ground about 9.30pm yesterday.

She had lost a large amount of blood and appeared to have been attacked with a knife.

Emergency services treated the woman at the scene before she was taken to Westmead Hospital. She died as a result of her injuries just after midnight.

Police said they believe the woman was attacked on her way home from work after leaving Parramatta train station, walking along the well-lit Argyle Street and up to Park Parade before taking the laneway which connects to Amos Street.

Police are yet to establish whether the attack was targeted or random but have urged residents to go about their lives taking only their usual precautions.

"It's a horrific attack without any stretch of the imagination and certainly my heartfelt condolences go out to the family at this point in time," Superintendent Wayne Cox said.

"There was a large amount of blood so she obviously suffered a significant wound."

He said police believe they know who the woman is but she is yet to be formally identified.

Contact is being made with the family before any personal information is released but it is believed she lives in the Westmead area.

A post-mortem is being conducted this afternoon.

Emergency crews scour the scene. (9NEWS)

The laneway connects to Amos Street. (9NEWS)

Emergency services assess the scene where a woman was found seriously injured last night. (9NEWS) (9NEWS)

Police are appealing to witnesses to come forward, particularly anyone who was on Argyle Street or Park Parade yesterday evening.

Anyone in the area at the time should contact Crime Stoppers on 1800 333 000.