A 20-year-old woman was knocked to the ground by a Nissan Patrol while walking on Fernleigh Road on Saturday morning, police have been told, before she was hit again by a different car.

The 19-year-old man behind the wheel of the Patrol had stopped to help the woman after she was initially struck near Glenfield Road.

It was while he and his passenger were assisting her that the second car hit her and failed to stop, police said.

The woman was treated at the scene by paramedics before being taken to Wagga Base Hospital with serious head and pelvic injuries.

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She was airlifted to Sydney's Royal North Shore Hospital, and police say she is being treated for "extremely serious life-threatening injuries".

Police issued an appeal for witnesses and dashcam footage on Saturday, which led to an arrest being made in Wagga's suburbs on Saturday.

A 19-year-old woman was arrested at a Glenfield Park home around 5.30pm on Saturday, and a black Honda City sedan was also seized for further examination.

The woman has since been released while investigations are ongoing, however Superintendent Noble said it was "highly likely" that charges would be laid pending further inquiries.

Superintendent Noble said police were still asking for anyone with any information, CCTV, or dashcam footage related to Saturday's events to come forward.

He also warned young drivers and pedestrians to remain extra-cautious while out late at night, when visibility is low and the chance of accidents is high.

"There is one common feature of all the people who were allegedly concerned in this matter: they were all young people, they were all out well and truly after midnight on the weekend with the operation of a motor vehicle being a feature," Superintendent Noble said.

"I would say to people: whether you're operating a vehicle at that time of the night or if you're a pedestrian, exercise extra care because clearly in circumstances like that the chances of a tragic outcome are much higher."

The driver of the Nissan was taken to hospital for mandatory testing after the incident, and the vehicle has been examined by specialist officers from the NSW Police crash investigation unit.

Anyone with information about this incident is urged to contact Crime Stoppers by calling 1800 333 000 or visiting the online reporting page.

Riverina Police District personnel are due to provide a further update this morning. We'll have updates here.