The met service expanded the yellow weather warning for high temperatures until 5pm on Tuesday.
Temperatures were expected to reach 41C inland, and around 32C in the mountainous areas. The minimum temperatures inland and around the coasts are not expected to drop below 26C, the met service said.
The warning came into force at 6pm on Monday.
On Wednesday, temperatures are expected to vary in the same levels, with a small chance of isolated showers in the mountain areas in early afternoon, according to Kitasweather.