Wellington builder Peter Rowe and his boss were going through a can of spray-on sunscreen between themselves every couple of days.
Rowe said 60-70 per cent of his workday was spent in the sun.
"The few times I've been sunburnt this summer it's because we've quite literally run out of sunscreen by about midday, which means, you know, the last half of the day you're exposed."
Worksafe's general manager for operations Jo Pugh said the heat had been "really brutal" on workers this summer, particularly those wearing "hefty protective gear" and those who were constantly in the sun.
There was no legislation in New Zealand to allow workers off once the temperatures reached a certain level, but managers had a duty to identify and deal with risks in the workplace, including those from heat.
Pugh said it was important workers recognised the signs of heat stress and tell a supervisor "before it becomes critical".
People needed to watch out for heatstroke, which can cause headaches, cramp, vomiting, dry mouth, and even death. Skin cancer was also something to be aware of.
Preliminary data shows the country's average temperature for the first 23 days of the month has been 19.85C — more than 2.72C higher than the current record.
That dates back almost two decades to February 1998 with an average high of 19.61C.
Niwa meteorologist Chris Brandolino said if temperatures held for the remaining eight days, long-standing records would be smashed.
"If things hold for January 2018 you would have the warmest temperature on record of any month and the largest difference from average ever," said Brandolino.
Climate scientist Dr Jim Salinger is going one further, calling it a done deal.
Waiau in Northern Canterbury hit a blistering 37C yesterday, the hottest temperature recorded for New Zealand in seven years.
Meanwhile Hanmer Forest, also in Canterbury, reached 36.2C.
Waiau's high was also the warmest January temperature recorded in New Zealand in nine years since Culverden also reached 37C in January 24, 2009, said the National Institute of Water and Atmospheric Research.
Kiwis across the country have been suffering through sleepless nights and some retail stores are running out of fans to keep up with demand.
The Warehouse GM of General Merchandise Jenny Epke said they had a limited number of fans in stock and would bring in more in time for February.
"We've sold double our usual number of fans so far this year."
Noel Leeming's EGM of Merchandise Jason Bell said stock was now "very limited" due to a huge uplift in demand for fans this summer.
"In fact over the past few weeks demand has been double that of the same period last year," he said.
"Dehumidifiers and air conditioning units are also proving popular as Kiwis tackle the humidity."
Online, the number of people searching for fans was climbing alongside the temperature.
Metservice Meteorologist Tui McInnes said most of the South Island would simply not be able to escape the heat over the weekend.
The high for Wanaka was set to be 31C today and 33C over the weekend before hitting 34C on Monday. Reefton was predicted to hit a high of 31C today and tomorrow before hitting 33C on Sunday.
The high in Auckland was set to be 27C today and 28C over the weekend.
Taumarunui is predicted to be the country's hottest spot, with a high of 33C
TOP TIPS FOR STAYING COOL:
1. Stay hydrated throughout the day. Simple advice, but mum is always right - drink lots of water to ensure you stay hydrated.
2. Freeze. It might sound a bit quirky, but putting your sheets or pillow in the fridge is said to be very effective. Take them out when you're ready for bed and enjoy a cool sleep.
3. Keep the curtains, particularly in the bedroom, closed during the day. It will keep the sun out. Open the windows in the evening when the air is cooler.
4. Fill a hot-water bottle with cold water and place it in the freezer. Place it under your feet or use it when you go to sleep. If it's too cold, cover it with a light cloth or hand towel.
5. Place a bowl of ice in front of an electric fan for even cooler air.
KEEPING PETS COOL:
1. Take your pet to a groomer or vet for a haircut for the summer. Then they can enjoy exercise times rather than lying around trying to stay cool all day.
2. Frozen treats: Rubber chew toys that can be filled with treats can be frozen overnight for your furry friend. Make ice blocks by freezing a bowl of water with dog biscuits or other treats inside. The frozen goodies act not only as a treat but as an activity for your pet.
3. Take your pet for a swim. Simple and fun.
Today's forecast
Whangarei: Sunny spells, chance afternoon or evening showers. Light winds. High 28C Low 19C
Auckland: Cloudy and chance drizzle then sunny spells. Light winds. High 27C Low 19C
Hamilton: Cloudy then sunny spells. A few afternoon and evening showers, with possible thunderstorms. Light winds. High 30C Low 18C
Tauranga: Fine, apart from morning cloud, and chance afternoon showers. Light winds. High 27C Low 20C
Napier: Mostly cloudy, chance drizzle then sunny spells. Morning southerly change. High 28C Low 20C
Wellington: Cloudy with drizzle then sunny spells. Southerlies. High 22C Low 18C
Christchurch: Drizzle becoming fine. Northeasterly developing in the afternoon. High 22C Low 16C
Dunedin: Cloudy then fine. Northeasterly developing in the morning. High 21C Low 17C
