Snow to sea level, record-low temperatures and ruined crops in Central Otago are possible as a cold blast hits the South.
MetService meteorologist Angus Hines said a "bitterly cold polar outbreak" is expected to bring a return to wintry conditions today as cold air from the Antarctic moves up the South Island.
Snow is forecast to 200m throughout Otago and Southland and is expected to dip to sea level in the afternoon, Hines said.
Flurries in central Dunedin are possible, with effective temperatures of about 2C to 3C.
The cold weather is expected to continue into tomorrow, before turning mostly fine by Friday, although temperatures will remain low over the weekend.
Such an early-October cold snap was uncommon and there was potential for record-low temperatures, Hines said.
In Invercargill, today's maximum temperature is forecast to be 6degC. The lowest previous October temperature was 5.8degC, he said.
A heavy snow watch is in place across the South and snow warnings are in place on Dunedin's Northern Motorway (State Highway1), Milford Rd ( SH94), Crown Range Rd and in the South Island's alpine passes.
Cromwell fruit grower Simon Webb said dealing with the cold snap was different from the inversion frosts which often affected orchards.
Because it was cold air, frost-fighting wind machines would not work as well as systems that worked by sprinkling water over fruit, which most orchardists did not have.
For those orchardists, "if it's blowing and it goes below zero, there's nothing you can do", Webb said.
The worst-case scenario for affected areas was that vulnerable fruit could be killed off and orchardists would have to wait another 15 months for the next crop, Webb said.
Central Otago high-country farmer Andrew Paterson said he had been getting recently shorn stock into sheltered paddocks, along with ewes and lambs that were being shepherded.
Other high-country stock would have to find their own shelter, as it would do more damage moving them once they had started lambing, Paterson said.
Southern district road policing manager Inspector James Ure urged people to drive to the conditions by increasing following distances and allowing extra time.
Waka Kotahi NZ Transport Agency journey manager Tresca Forrester said drivers should monitor weather forecasts and pack warm clothes and food if they were travelling.
Extra care was also needed for driving high-sided vehicles or campervans because of expected high winds, Forrester said.
Dunedin deputy electoral officer Clare Sullivan did not expect major disruption to local body voting.
An NZ Post spokesman said any voting papers received by councils by noon on Saturday would be deemed to be eligible.
Any ballots not delivered to councils or the two election counting organisations, Election Services and Electionz.com, because of weather would be invalid.
If a council required extra time because of weather, the electoral organisations could decide to make an application to extend the voting period, he said.
Two proposed residential development sites in Havelock North were removed from the FDS.