A house lost its roof and conservatories collapsed as a "severe" hailstorm hammered Christchurch.

Brilliant displays of lightning and roaring thunder were followed by "golf-ball sized" hailstones across the city. Hailstones in some suburbs measured about 3cm in diameter.

A fire service spokesman said crews attended more than 20 storm-related incidents between 6.30pm and 7.30pm.

"We had callouts relating to alarms being activated by water getting into the system and we helped some people make their houses weathertight too," he said.

Conservatories collapsed in Hornby and Redwood, he said. "We investigated a couple of lightning strikes on properties but there's been no reports of fire."

Lightning knocked out power in Southbridge and Leeston about 6.30pm.

Mainland taxi driver Rick Sun said he was taking a fare down Sawyers Arms Rd when he thought someone had thrown a rock at his windscreen.

"It hit hard. I have been hit before by a beer bottle and I thought ‘not again'."

Then the hailstones had smashed onto the car roof, sounding like a hail of rocks.

His passenger had got out to take a photograph of the "golf-ball sized" hail stones but had been hit on the head and was soon back in the car.

The hailstones had made small dents all over the roof and bonnet of the car, he said.

He had seen nothing like it in his 10 years in New Zealand.

Met Service weather forecaster Allister Gorman said hailstones larger than 20 millimetres put the storm in the "severe" category.

"Thunderstorms were on the radar for the Canterbury plains but we weren't sure whether it would hit the city . . . obviously it has and that would be a first in quite a while, I would imagine."

There were about 300 lightning flashes in Canterbury, Gorman said.

"It's the sort of storm we would typically see in the summer but it's been a while since the city of Christchurch had one," he said.

One Jet Star flight from Auckland was delayed by half an hour. Press science reporter Paul Gorman, who lives in Ilam, said the hailstones sounded like "gunshot blasts".

He said it was "one of the only times" he had been scared by the weather.

Facebook user Garry Thomas said Mother Nature was obviously "not a big fan of September 4", the anniversary of Canterbury's 7.1-magnitude quake.

The storm had developed over the Canterbury Plains near Ashburton Tuesday afternoon and moved northeast blown by a southwest wind.

Thunderstorms also occured in Buller, Northland, south of Wellington and the Waikato on Tuesday.

-  A previous version of this story reported that the storm had developed over Weka Pass about 2pm.

- © Fairfax NZ News