A severe thunderstorm warning has been issued this afternoon by MetService, with gumball-sized hail falling in South Canterbury and a funnel cloud sighted.
MetService said a severe storm was detected about 12.15pm in the area of Ashburton and Timaru.
A severe thunderstorm watch remains in effect for Christchurch, the Canterbury Plains and high Country, as well as North and Central Otago.
Timaru and Oamaru locals provided photos showing extremely large hailstones, with several also sighting a funnel cloud forming near Oamaru.
Brad Dennison of Timaru said the hail was so large that it punctured holes all over the clear roofing at his workplace.
"It hit about bang on 12. The first few stones came straight through the roof," said Mr Dennison.
"We're up on the roof covering up the holes and clearing the gutters before another one comes through."
He said from where he is, he can see people on roofs all around.
"The neighbours are all rallying together."
Canterbury Police tweeted that people should stay inside, and that if they were driving at the time a storm hit, they should put their phone away.