An 8-year-old girl has survived two hours in the back of a submerged car in an accident that killed her brother.

The 10-year-old West Coast boy drowned after the car he was travelling in rolled into a pond near Hokitika.

The crash happened about 7pm yesterday at a private goldmine near Ruatapu, about 12 kilometres south of Hokitika.

A man who worked at the mine in Adair Rd was with his children when his four-wheel-drive rolled and became almost submerged upside down in a slurry pond.

He escaped and ran about 2km to a relative's house to raise the alarm.

The girl survived after finding an air pocket near the back of the car.

She was rescued after almost two hours and taken by rescue helicopter to Grey Base Hospital in Greymouth with hypothermia.

Her father was also taken to hospital.

The boy's body was removed from the car last night, with his family at the scene.

West Coast area commander Inspector John Canning said the family was "grieving pretty badly".

The girl's rescue prevented an even greater tragedy, he said.

Canning said the children's father took his son and daughter to the West Coast mine where he worked yesterday to refuel pumps used to remove water from the mine's open pit.

While driving his four-wheel- drive Toyota Hilux, it rolled into the crater and became submerged upside down with only part of the car's rear above water.

Canning said the man managed to get free and ran several kilometres along Adair Rd to a relative's home to alert emergency services about 7pm.

It was unclear what rescue attempts he made.

About 10 or 15 minutes after police arrived, an officer heard a noise in the rear of the car and found the girl still alive, where she had pulled herself to breathe from a small air pocket.

She was quickly pulled out and taken to Grey Base Hospital after her family rushed to the scene to see her. "They were here just in time to see her."

Canning said the girl looked shocked to be found, and was very cold and wet after spending almost two hours trapped in the vehicle.

However, her brother's body was later removed from the car.

"They are grieving and they are grieving pretty badly," Canning said.

He said he was yet to speak to the father, who was in shock.

It was the second fatal car crash on the West Coast yesterday.

An investigator from Blenheim attended a crash at Ngahere at 4.30am.

The investigator had just returned to his motel after dealing with that crash when he was called to the mining tragedy, Canning said.

- © Fairfax NZ News