Dunedin is officially having its hottest day on record, hitting 35 degrees celsius.
MetService forecaster Cameron Coutts said the heat was recorded at the airport at 3.12pm today.
The city's previous hottest day was 34.9°C, and its previous hottest January day was 34.7°.
Records go back to 1972.
Our weather station at Dunedin Airport recorded 35C at 3.12pm today (minute data), which would make this the hottest day on record for Dunedin Airport since records began in 1972. ^Lisa pic.twitter.com/N5wKm6FBz7— MetService (@MetService) January 16, 2018
Mr Coutts said Dunedin was the hottest place in the country today, but noted the city would be slightly cooler than at the airport.
Southern District Health Board made a plea yesterday for people to keep cool, when 30 people went to hospital after the mercury hit 32.3° in Invercargill, its hottest on record.
Deputy chief medical officer Dr Tim Mackay said Invercargill had another eight people show up in hospital because of the heat today, mostly children with sunburns.
"So it's just about making sure that kids get some sunscreen on," he said.
"One of the other problems that tends to happen now when you've had a couple of hot nights is it can start to affect the elderly so it's best to keep an eye on older people."
The hot and dry weather is driving river levels in Otago to new lows, with one site in the region at its lowest since records began in 1982.
NIWA's drought index shows the district is "extremely dry", with temperatures hitting 33° in Alexandra today.
Otago Regional Council manager of environmental services Martin King told RNZ the low flows were starting to hurt the environment and the local community.
MetService is predicting some rain for Thursday but Mr King said the region needed a more sustained downpour to help replenish the rivers in a sustainable way.
Compulsory restrictions may be enforced if residents did not conserve water, the council said.
Council water manager Tom Dyer said water levels in the city's catchments were dropping while demand was increasing.
If rain did not fall this week and demand continued, the city would need to move to the first level of compulsory restrictions before the weekend.
Voluntary restrictions have been in place in the city since early December, but water use is now more than 35 percent above normal.
Watch Dr Mackay's tips for staying cool:
Dr Mackay urged people to drink at least two litres of water per day, use their heat pumps for air-conditioning or get cool, damp towels on the backs of people's necks to cool them down.
"Dehydration can occur quite quickly, and with these hot conditions being less common in Southland, it's possible people are not as quick to pick up on the symptoms," he said.
"We ask people to de particularly careful about the effects of drinking alcohol in the hot weather. Far from quenching your thirst it will speed up dehydration, and can be quite serious."
Fire and Emergency have imposed a total fire ban across Otago from midnight on Monday.