Two men have died after a sudden turn in the weather caused waves to swamp their kayaks, tipping them into the icy cold water in Lake Tekapo this afternoon.

The pair, believed to be visiting from overseas, were part of an eleven-member group that had gone out onto the lake.

The remaining nine were pulled from the water alive and were treated for hypothermia - two were sent to Timaru hospital, via ambulance, in a serious condition.

Mid-South Canterbury Area Commander Inspector Dave Gaskin says when the group first went out the weather was calm.

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But he says they were hit by a north westerly at speeds of around 40k/hr.

"The boats were swamped and they were tipped into the water."

He said it was about three degrees in the water and with the winds it would have been even colder.

Mr Gaskin said emergency services were alerted to the accident at about 4:30pm, by which point it's thought the group, of men and women, had been in the water for about an hour.

He says a local man who had hired out the boats made the call after seeing the change in weather.

"He tried to go out in the boat, but the waves were too high."

Mr Gaskin wouldn't confirm if the two deaths were due to hypothermia but says all members of the group had been wearing life jackets at the time.

He said a group of local volunteers and emergency service workers retrieved the nine surviving kayakers, some from a nearby island, and the two deceased from the lake.

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Mr Gaskin says the tour group was from overseas - but wouldn't divulge from where.

He says it was not unheard of for the weather conditions on the lake to change so quickly.

"Lake Tekapo is very dangerous."

Lake Tekapo Canterbury at about 5.30pm this evening. Photo / Supplied
Lake Tekapo Canterbury at about 5.30pm this evening. Photo / Supplied

According to MetService the weather in Tekapo was cloudy today with inclement weather expected later this evening. There were no severe weather warnings in place.

A local resident, who did not want to be named, says the first he'd heard of an accident was when the fire siren went off just after 5pm.

He says there had been a very strong wind that afternoon and the lake had been extremely rough.

One News named the company the kayakers were on the lake with as Aquanorts.

According to their website Aquanorts do not operate on "severe windy and rainy days".

If the status is closed due to wind please understand that it is for safety reasons as the wind is a lot stronger on the Lake and the waves the wind create can be deceiving when viewing from the beach. Please understand our decision. Thank you.

On Thursday at 9.30am the company updated the site, listing it as open for the day.

When contacted by the Herald a woman tearfully declined to comment.

Tourist reviews for Aquanorts are positive.

On the website Tripadvisor, a recent visitor from Melbourne said: "Even if you have gone kayaking before, this is not to be missed. The clear blue water and the amazing atmosphere make it a must do option".

In December another visitor said Aquanorts offered "the best way to see" the lake.

"The instructor is a top bloke and is more than happy to talk you through each watercraft on offer and give honest recommendations."

Mackenzie District Mayor Claire Barlow says she has limited information, but it had been a "terrible week for Mackenzie".

"Very sad indeed," she wrote on Facebook.

Lake Tekapo is in the Mackenzie District about 245 km south west of Christchurch.

The area is famous for recreation activities including tramping, mountain biking, climbing, horse trekking, fishing, hunting, boating, kayaking, scenic flights, star-gazing, skiing, heli-skiing, ski touring, cross-country skiing, ice skating, water-skiing and windsurfing.