According to the MetService website, the temperature in Dunedin reached 26degC at 1.30pm and hovered around that until 3pm, when Hastings took over as the hottest place in New Zealand.
An unofficial temperature gauge at Otago Museum recorded a temperature of 30degC at 3pm.
MetService meteorologist Ciaran Doolin said the temperatures spiked due to a phenomenon known as the fohn effect, which happened when there was a west/northwest flow.
"The air gets forced up over the divide and precipitates out its moisture as it goes over the ranges.
"As it comes down the other side it's quite dry and it warms.
"So you get a dry, warm wind and typically quite strong as well.''
A lack of cloud cover in Dunedin pushed the temperature up further.
It was unusual for Dunedin to be the warmest place in the country in spring, but the fohn effect was in play.
He said Dunedin could expect a typical spring "mixed bag'', with close to normal temperatures likely for the rest of this month.
This was evident on the MetService website with temperatures of 12degC and 13degC and some rain predicted for Labour Weekend.
Rain is expected in Otago today but temperatures would remain mild, around 18-20degC.
