Temperatures exceeding 40C are being reported in parts of Christchurch.
Christchurch based weather analyst Richard Green said thermometers reached 40C in the early afternoon with the suburb of Barrington reaching 41C, 40C in Cashmere and 38C in Christchurch city.
The official MetService temperature in Christchurch at 2pm was 34C.
"This is like being in the outback of Australia," said Green. "It's been quite some time since I've experienced heat like this".
The warm weather comes as the National Institute of Water and Atmospheric Research (Niwa) today forecast above average temperatures across New Zealand through to March.
NIWA said it was likely to be drier than average in the south, but rainfall in the north was expected to be normal or above normal.
Niwa predicted more easterlies than normal in the north but lighter winds than normal in the south.
Moderate La Nina conditions were likely to continue into autumn, it said.
There was a slightly higher chance of an ex-tropical cyclone passing within 500km of the country during the cyclone season through to May.
- NZ HERALD STAFF, NZPA