A female bushwalker is missing and there are grave fears for her safety after she was swept down a river on the Milford Track in Fiordland on Monday.

There has been no sign of the 22-year-old tourist since 6pm when the incident happened at 3pm.

Senior Sergeant Cynthia Fairley said the woman was walking the track with her Australian partner when it appeared she became caught up in the Pompolona Creek at around 3pm yesterday afternoon and was swept into the Clinton River.

Her male companion had activated a beacon yesterday after the incident occurred.

The Rescue Coordination Centre attempted to send a Southern Lakes Helicopter to Pompolona Lodge but the helicopter needed to turn back due to adverse weather conditions, Fairley said.

This morning at around 7.30am a helicopter and observer search crew visited the area, searching the Clinton River and surrounds but did not find anything of significance.

Fairley said Pompolona Creek has a heavy flow due to recent rainfall and weather conditions in the area are poor with rain continuing to fall this afternoon.

The conditions were such that a foot search is not feasible. It's planned that a further aerial search would be conducted this afternoon.

Police were working with local Department of Conservation staff and local LandSAR volunteers to ensure that they had the best possible knowledge of the search area and conditions.

The pair was visiting New Zealand and walking the Milford Track after spending some time in Queenstown. Police are not able to release the nationality of the woman involved.

The male tramper is helping police with the search effort and is being supported by Victim Support.

Rescue Co-ordination Centre New Zealand (RCCNZ) spokesman Michael Flyger said a beacon was activated by an Australian party of three about 6pm yesterday, near Mintaro Hutt on the track.

Grim weather prevented a helicopter reaching the area last night but a police team was flown to the hut this morning.

It has been reported one of the group is missing, he said.

There had been a lot of rain in the Fiordland and the rivers, including the Clinton River, were very high and fast-flowing, Flyger said.

The RCCNZ was working with Te Anau police to get more information from the tramping party.

The Milford Track is one of the country's most popular tramps, and is listed as one of New Zealand's nine great walks by the Department of Conservation.

Weather in the area is poor, with the MetService issuing a severe weather warning at 9.02am today.

A series of fronts are forecast to bring heavy rain to Fiordland today and for part of tomorrow.

Heavy rain fell in Fiordland yesterday and a further 180 millimetres to 220mm was expected over the next 24 hours.

MetService said rivers and streams might rise rapidly and surface flooding and slips were possible.

- Stuff