Surf Life Saving reports no lifeguards are on duty at this time of year and there is a heightened risk people might get into strife.
"We ask that members of the public avoid recreating in and around the water for the small period that the increased swells and tides are in effect and to be cautious and use common sense," a spokesman said.
There would be extended response times to help anyone who came into trouble, he added.
If anyone gets into trouble, people should call 111 and ask for the police.
Potential water-users are asked to never surf, swim or fish alone at any time - but especially in these conditions.
Weather
Meanwhile, strong winds, heavy rain and snow are set to hit parts of the South.
MetService says an active cold front is forecast to move quickly eastwards across the country on Friday, bringing strong southwesterlies, while an associated deep low also moves eastwards to the south of the South Island.
Up to 35cm of snow is forecast for the Milford Rd in Southland, up to 10cm on the Crown Range Rd, linking Queenstown and Wanaka, and up to 20cm to fall on the Lewis Pass in Canterbury.
The Milford Rd will close on Thursday at 4.30pm from the Hollyford Rd Junction and at 5pm from the Chasm.
Heavy snow is forecast for the tunnel area overnight and through Friday, the New Zealand Transport Agency advised. This closure is likely to remain throughout Friday and overnight into Saturday due to the significant snow event.
Delays and closures are possible through the weekend, with continued snow forecast.
A period of heavy snow is forecast for Fiordland and southern parts of Otago above 500 metres, and a heavy snow watch is in force.
Snow is forecast for alpine passes in the South Island.
Heavy rain is also expected below the snow level in Southland and Clutha, and a heavy rain watch is in force.
Strong winds
The strongest winds are expected to be in the south, with warnings in force for Fiordland, Southland and Otago.
There will be severe south-west gales of up to 120kmh in Fiordland, Southland and the Southern Lakes from 9am to 7pm on Friday, MetService says.
Severe south-west gales of up to 120km/h are forecast for Otago from 11am on Friday until 2am on Saturday.
In Dunedin it'll be chilly on Friday, with southerly wind gusts up to 90km/h and periods of rain in the afternoon, bringing possible thunderstorms and hail and a high of 10C.
Oamaru will also get rain with possible thunderstorms and hail and strong winds up to 110km/h and a high of 12C.
Heavy rain is forecast to hit Queenstown, while Wanaka and Alexandra will also be wet and all have a high of 9C.
Thunderstorms and hail are likely for Invercargill and a high of 10C.
Boaties are warned there will be a significant swell approaching the country from the southwest on Friday, with waves 8m-10 metres off the west coast of the South Island.
People are advised to keep up to date with the latest warnings and watches in case any changes are made, or other areas added.
Snowy roads
MILFORD RD (SH94)
Between midnight tonight and 2pm on Friday, expect 25cm to 35cm of snow to settle on the road above 700 metres, with lesser amounts down to 500 metres.
CROWN RANGE RD
Between 2pm and 11pm on Friday expect 6cm to 10cm of snow to settle on the road above 700 metres, with lesser amounts down to 500 metres.
LEWIS PASS (SH7)
Between 9am and midnight on Friday expect 15cm to 20cm of snow to settle near the summit of the road, with lesser amounts down to 600 metres.
ARTHURS PASS (SH73)
Between 9am and 9pm on Friday snow showers are predicted, and 3cm to 6cm of snow may settle near the summit of the road, with lesser amounts down to 600 metres.
LINDIS PASS (SH8)
Between 3pm and 11pm on Friday, 1 to 3cm of snow may settle on the road above 700 metres, with lesser amounts down to 500 metres.
- additional reporting Otago Daily Times
