The thunderstorm that has lashed the South Island and brought widespread and large hail is one of the year's most intense storms, MetService says.
Large parts of the mainland have been under brief severe thunderstorm warnings through Saturday afternoon.
Selwyn and Ashburton are currently still under severe thunderstorm warning.
Other parts of the South Island including Timaru, Christchurch city, Central Otago, Southern Lakes, Dunedin and Southland are under a severe thunderstorm watch until 9pm on Saturday.
At one point NZTA dispatched crews to State Highway 8 between Timaru and Fairlie after reports of hail blocking the road, and cars getting flooded.
"There has been some very active weather in parts of the South Island, that east and south eastern area, all the way down to Southland, Clutha, North Otago and Dunedin and up the Canterbury coast as well, there's been lots of lightning, lots of thunder and also hail," MetService meteorologist Devlin Lynden said
"We've seen reports of widespread hail particularly in that Canterbury Plains area, as well as very long-lived thunderstorms and heavy downpours in that Canterbury area."
He said storms like this could happen at any time of year.
"Particularly in summer, it's often we see thunderstorms in summer," he said.
MetService confirmed that the most severe hailstorms have been from a supercell storm in the southern Canterbury Plains region, which is a powerful thunderstorm with a rotating updraft.
"This rotation allows the storm to last longer and become more intense than typical thunderstorms, increasing the risk of severe weather such as large hail, damaging winds, and heavy rain," MetService said.
"That was some hail storm this afternoon!" Ashburton District Council said in a Facebook post.
It said its roading maintenance contractor was out after the hail storm clearing street gutters to make sure stormwater could drain away.
Horticulture New Zealand's regional representative, Chelsea Donnelly, said there had been no reports so far of any damage to crops.
Two farms near Ashburton contacted by RNZ said the severe hail storms did not reach them.
MetService had said that very heavy rain can cause surface and/or flash flooding about streams, gullies and urban areas.
Poor visibility and surface flooding could make driving difficult, and large hail had the capacity to "cause significant damage to crops, orchards, vines, glasshouses and vehicles".
"Should severe weather approach or if you feel threatened, take shelter immediately."
