The 56-year-old woman was taken to hospital with serious cuts to her face and body after she was attacked while sitting in her car in Dundas, near Parramatta, on Thursday night.

Police said she had been driving along Kissing Point Road in her white Mitsubishi Lancer about 10pm and turned in to Rippon Avenue to make a call on her mobile phone.

As she sat in the car, a man she did not know approached and began hitting the vehicle with a shovel.

The woman told police the man screamed at her to get out of the car, which she refused to do.

The man then allegedly forced open the driver's side door and began hitting the woman on the face and arms with the shovel, before stealing her mobile phone.

The woman escaped in her car and drove to a nearby petrol station on Church Street in Parramatta.

She was bleeding from the face when she entered the petrol station and asked staff to call police.

A NSW Police spokesman said the woman was traumatised and was treated by paramedics before being taken to hospital.

Police set up a crime scene on Rippon Avenue on Thursday night and searched the area with the assistance of a police dog.

About 10.45pm, officers arrested a man on Rippon Avenue. He was carrying a mobile phone.

The 32-year-old man was taken to Parramatta police station and later to Westmead Hospital, where he remained under police guard on Friday morning.

Police are continuing to investigate the assault. No charges have been laid.