Six people have been airlifted from the area of an ultra marathon event near Arrowtown and others have activated emergency locator beacons.

Maritime New Zealand was first alerted to the developing situation following a beacon being activated at 1am, it said.

The Rescue Coordination Centre said nine beacons were activated between 1am and 9am.

Operations manager Michael Clulow said the six people who were airlifted out had been taken to Queenstown Lakes Hospital.

They were suffering from mild hypothermia.

A spokesperson for Queenstown Lakes Hospital said they were all in a stable condition.

At least 110 people are in the area associated with the ultra marathon, Clulow said.

At this stage the majority of competitors and staff had been accounted for and were safe at the Macetown Camp area, he said.

The priority was reconciling the number of people in the area and confirming they were safe.

A statement on the Facebook page of the Southern Lakes Ultra Marathon said a rescue operation was underway for participants and crews, but at this stage all athletes were safe, well and accounted for.

Heavy rain has caused the Arrow River to rise and bad weather was forecast to continue.

MetService said the weather in the Queenstown area was fine when the ultra marathon began on Sunday, but a cold front subsquently moved in.

Meteorologist Amy Rossiter said the front was accompanied by unseasonably cold weather and brought snow to above 1200 metres.

Up to 60mm of rain fell in the ranges in a 24-hour period, she said.

The rain was expected to ease to showers on Thursday with fine weather forecast for Friday.