A woman suffered spinal injuries on Monday morning after the jet ski she was riding plunged into a sand bar at Wallaga Lake, on the coast south of NSW.

NSW Ambulance Officers and lifesavers treated the woman, aged in her early 20s, at the scene in Bermagui, and the Snowy Hydro SouthCare helicopter took her to Canberra Hospital where she remains in a serious but stable condition.

Surf Life Saving duty officer Andrew Edmunds said three people were on the jet ski when the accident happened, and two people were thrown to the ground.

One of the other riders landed on top of the injured woman.

Mr Edmunds said lifesavers had attended several accidents involving jet skis over the summer, and warned people to be careful when using the vehicles.