A severe thunderstorm watch has now been lifted for Christchurch, but remains in place for the Canterbury Plains, Canterbury High Country, Marlborough, Wellington, Wairarapa, Kapiti-Horowhenua, Tararua, Manawatu, Hawke's Bay and Gisborne.
In Christchurch, Fire and Emergency New Zealand said heavy rain had flooded houses in the suburbs of Belfast and Middleton.
Four flights have been cancelled and others delayed at Christchurch Airport, where MetService said sensors detected 2mm of rain falling in just one minute.
An airport spokesperson said lightning strikes had affected airfield lighting and navigation systems, although the airport was still open.
Three fire crews were responding to a hedge fire in Yaldhurst sparked by lightning about 10:15am.
MetService meteorologist Lewis Ferris said the risk was mainly for the heavy rain, large hail and strong wind gusts, making driving conditions hazardous.
"That hail did really decrease visibility so if you happen to be out driving out in a severe thunderstorm or a thunderstorm with hail in your path maybe slow down, maybe even pull off the road, it will pass," he said.
MetService warns that large hail which can come with thunderstorms can cause significant damage to crops, orchards, vehicles and glasshouses.
