Three people have died tramping in the South Island in the past 24 hours.

Two tourists have been killed while trying to cross a river near the West Coast's Franz Josef Glacier, while a man man has fallen to his death while tramping in Kahurangi National Park.

A group of four tourists were on a walk near the glacier at about 9.30pm yesterday, when they went off the walking track in the dark and tried to cross the Waiho River on foot.

Two of the group, a 20-year-old woman from China and a 23-year-old woman from Malaysia, were swept off their feet and washed down stream.

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The other two walked out of the bush and raised the alarm, and the Solid Energy Rescue helicopter was called in to search at midnight.

The helicopter's pilot, Angus Taylor, said the first woman's body was spotted after 45 minutes of searching, about a kilometre upstream from the State Highway 6 bridge in Franz Josef and several kilometres from where the group had tried to cross the river.

The second body was found another kilometre down stream.

Mr Taylor said searchers had been hoping to find the women alive.

"The river was not deep, it was low flow, but there was also a combination of darkness, dirty water coming straight from the glacier, lots of bolders, and super cold.'' he said.

"They couldn't see where they were putting their feet, and lost their footing, then all it takes in shallow water like that is a bang on the head.''

Police are still working to contact the women's next of kin, and said the deaths had been referred to the coroner.

Meanwhile a Nelson man has fallen to his death while tramping in Kahurangi National Park.

John Leo Hannah, 63, was tramping with two others in the Adelaide Tarn area of the park last night, when he slipped on difficult terrain and fell 20 metres to his death, Senior Sergeant Stu Koefoed of Nelson police said.

"Police are speaking to the members of the tramping party to ascertain the full circumstances relating to the death of Mr Hannah and will then refer the matter to the Coroner.''