Rotorua is expected to reach "heat wave conditions" in the coming days.
MetService meteorologist Kyle Lee said in New Zealand a heat wave has been defined as five consecutive days where a place reaches five degrees above its average temperature for that time of year.
"Rotorua and Whitianga are on track to reach these conditions as a ridge of high pressure holds its ground to start the week ahead," he said.
"Similar weather is forecast until midweek when a front over the South Island gains some momentum and makes its way towards the North Island."
Rotorua reached 28.6 on Saturday and Tauranga was just behind at 28.4C.
Meanwhile, Tauranga made it into the high 20s every day last week, peaking with 29.4C on Thursday, the day the Tauranga City Council introduced a sprinkler ban.
Residents have been asked to completely stop using sprinklers and irrigation systems until further notice and only use hand-held hoses between 5am and 8am, and from 7pm to 10pm instead.
The city's water demand was up by 40 per cent on normal average water use, the council said.
Rotorua does not have water restrictions so far, but the Rotorua Lakes Council said: "with little rain since Christmas, consumption has been high in all of our water supplies for the last few weeks", leading up to the long weekend.
"It is important that people minimise water wastage, whether it is with garden or lawn watering, pool filling, car washing or any other significant use."
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Bay of Plenty residents have been making the most of the region's lakes and beaches to cool down.
The Hokianga family moved to Pāpāmoa from Auckland a year ago.
"Now we have the luxury of popping over to the beautiful lakes... Sometimes you just need that fresh water," Hazel Hokianga said.
"New Zealand doesn't get much better."
Blue Lake Top 10 Holiday Park duty manager Laura Leaf said between 700 and 800 people were staying at the park near Rotorua for the long weekend.
"A lot of guests are competing in the triathlon, and there have been lots of people on the beach."
She said the campground store had been kept busy with campground guests and lake visitors alike, wanting to buy icecreams and cool drinks.
"The shop is pumping when it's hot in summer."