More than 1600 lightning strikes have pinged the country in just two hours this afternoon - and MetService warns of many more to come as thunderstorms hit.
MetService recorded 1686 lightning strikes over a two hours until 3pm today, including a "humongous cluster" near Dannevirke.
MetService meteorologist Tuporo Marsters expects more strikes this afternoon and evening.
"She's climbing. Most of them are right through the middle of the North Island, and the Canterbury region, close to Timaru, has had a bundle of sparks go off, and inland Dunedin."
A severe thunderstorm watch is in place until 10pm for a large chunk of the North Island - stretching from the Far North through Hamilton, across Hawke's Bay and to Masterton.
MetService has also issued a severe thunderstorm warning for Timaru and Waimate just after 3.30pm.
The thunderstorms are moving east and will lie near Timaru, St Andrews, Pareora and offshore east of Timaru by 4.07pm.
The thunderstorms are expected to bring more torrential rain and hail.
A similar warning remains in place for the Canterbury Plains and High Country, North Otago and Central Otago as well as Dunedin and Clutha.
Sandbag stations were opened yesterday in Dunedin as flooding hit.
Overnight Saturday, residents in Middlemarch were advised not to flush their toilets and avoid drinking water from bores as it was likely to be contaminated.
Residents in Middlemarch were today again asked not to flush toilets after a
a lightning strike cut power in the area about 2.30pm, meaning the town's sewerage system will not be able to operate efficiently.
"With rain again falling in the area there is a risk that wastewater flooding will occur," Dunedin City Council said.
Slips and flooding closed several stretches of state highways today, including part of SH2 in the Bay of Plenty, where the Waimana Gorge road between Kutarere and Tanetua closed as of 4pm.
Other key local roads in the area are also closed by flooding and there is no viable detour, NZTA said.
SH2 through the Waioeka Gorge, south of Opotiki, has recently reopened, however, caution is advised as heavy rain continues and the road may need to close again.
SH83 between Aviemore and Otematata in Canterbury will be closed until January 10 because of flooding.
"A detour route is available and is suitable for all vehicles," an NZTA spokesperson said.
Looking ahead to tomorrow, parts of the North Island are in for a third day of bad weather, Marsters said.
"We've got a moderate risk from the Bay of Plenty through to Gisborne and including the Hawke's Bay region for thunderstorms.
"It's not as severe as we had today, but there is a risk."
There is set to be some reprieve from the wet weather on Tuesday for most of the North Island and for the top of the South Island - but it's a different story for those in other parts of the south.
"We can enjoy some really nice weather for most of the North Island and the top of the South Island, but it's just the bottom bit again. We've got rain symbols from Fiordland to Invercargill," he said.
"The lower south west of the South Island, Fiordland, and down to Invercargill, we've got another rain system affecting those guys."