The boy who drowned in a goldmine pond on the West Coast last night has been named as Tayne Luca Bowes, 9.

Tayne was killed after his father's car flipped upside down in a waist-deep pond near Hokitika.

Two police officers have described their rescue of his sister from the submerged vehicle after she had spent nearly two hours in the water.

The children's father had taken them to the private gold mine where he worked on Adair Rd, just south of Hokitika on the same road as their home, to refuel a floating pump that drained the mine pit.

Police said today it was unclear how the car came to roll into the pond or whether the father had been in it at the time.

Afterwards, the father began to run to his home on the road but turned around and ran to a friend's place several kilometres away to alert emergency services about 7pm.

Sergeant Russell Glue, of Hokitika police, was first to the scene and spotted the Toyota Hilux four-wheel drive almost completely submerged in the pond, the pump still going.

He waded into the murky waist-deep water with colleague Senior Sergeant Allyson Ealam, office in charge of West Coast police response, to check the car, expecting both children would be drowned.

''I could see something floral in the car but I couldn't see any movement,'' Ealam said.

Glue smashed its rear window with equipment from the Hokitika volunteer fire brigade and they were stunned to hear the girl call out for help.

''We didn't expect to hear that cry,'' Ealam said.

''I thought we were hearing things. Fortunately we weren't and it was all on.''

The girl was gasping and gulping for air, blue with cold after being submerged for so long but had managed to breathe in a small air pocket at the vehicle's rear which was above water.

Glue pulled her out and quickly passed her to Ealam before continuing to search for her brother, desperately hoping he would follow her out but he didn't.

''I'll never forget her little face,'' Ealam said as tears welled in her eyes.

''It was like she had just woken up, she was shaking, wet and gasping.''

The freezing cold girl clung to them as she was passed to another colleague ''who had taken a leaping jump down the bank''.

The girl managed to smile at that police officer and said ''thank you'' to him before she was bundled up into the ambulance.

Her father returned to the scene a few minutes later and accompanied her to hospital.

Smashing the window probably nudged the girl awake, Ealam said.

The girl was taken to Grey Base Hospital last night suffering hypothermia but was discharged this morning.

Her brother's body was removed from the vehicle last night once it was lifted out of the pond and his mother spent time with her son at the scene.

West Coast area commander Inspector John Canning said the family was devastated at the loss of their son but elated with their daughter's survival.

''That wasn't a happy ending.''

The two children were pupils at Hokitika Primary School.

- © Fairfax NZ News