Police said the woman, aged in her early 30s, was riding the bike on her Middle Arm Road property, some 2.5km from Goulburn, when the vehicle went into a drain. The bike tipped over on top of her, causing significant internal injuries.

A child pillion passenger was not injured.

Family members contacted emergency services, but also loaded the woman into the back of their own vehicle to take her to hospital.

Motorists reported that the Hilux suddenly pulled over by the side of the road, with hazard lights flashing, and an occupant commenced CPR on the woman.

NSW Ambulance media said the woman had gone into cardiac arrest when a road crew met the family on the Middle Arm Road about 1.40pm. By that time other motorists had also stopped and assisted.

Ambulance officers took over resuscitation. A helicopter crew from Canberra was also tasked to the scene. Its medical team, including a doctor, also rendered assistance.

Ambulance conveyed her by road to Canberra Hospital. Police were advised on Monday that she remained in a critical condition.