The rainbow, as seen from Sumner.

The sun comes out following a brief shower over Christchurch.

A rainbow to the south of the city. Photo taken from the Leisure-Port at the airport.

A second tornado has swept through Amberley in North Canterbury, damaging homes, felling trees and bring down power lines.

Amberley resident Leanne McTear was on her doorstep when the tornado struck her home, ripping the roof off and hurling it across the road.

"Everything went dark and there was just black dust and smoke whirling around,'' she said.

"There was a horrendous noise and I was waiting for the ground to move. It was really noisy and I didn't know what was going on. I saw bricks on the front lawn and Pink Batts everywhere. At the moment I am quite numb.''

Weather enthusiast and stormchaser Stephen Burrows said he saw a tornado near Amberley and a house near State Highway 1 had its roof ripped off.

"The roof has been completely stripped off. The roof was on the other side of the road,'' he said.

Blue Skies forecaster Tony Trewinnard saw the tornado form and travel from north of Amberley for about two or three minutes.

He said it was traveling at about 70 kilometres an hour and hurled debris about 100 metres into the air.

"There is no doubt in my mind that this was a tornado,'' he said."It was definitely a tornado. It wasn't hanging around. It was moving quite fast.''

Donna Graham has lived in Amberley for 20 years but has ''never seen weather like it''.

Graham and her husband Geoff witnessed a tornado above Amberley and saw ''trees shredded'' before hail stones battered their house.

''I was really frightened...it was just so dark looking and it was so close.''

The Grahams house faces south and Donna Graham said she had watched the ''black clouds hanging over the city'' since the late afternoon.

''I said to my husband that they were the sorts of clouds that form twisters...and I just couldn't believe what we were seeing.''

The couple photographed the tornado and filmed a short video before they lost power and decided to drive to a neighbour's house.

She said debris started hitting her home and she was scared the windows were going to smash.

''On one hand, it's really magnificent but I was ready to hide in the cupboard if I had to.''Graham said the extreme weather had shaken her up.

''I just honestly have never seen anything like it,'' she said.

LEESTON TORNADO

A mini tornado briefly formed near Leeston during the storm as well.

Weather enthusiast and ''stormchaser'' Stephen Burrows said he captured the small tornado on his video camera.

''It looked like a tornado in the Leeston area. I could see some dust being kicked up around it. It seemed to be about 100 metres wide, but quite weak,'' he said.

''It reached down to the ground. It wasn't a traditional, American one where it is a direct line from the cloud to the ground, but you could see it reached the ground and it was full of dust.

Canterbury resident Inca Woodroffe saw the mini tornado from her home.

''I was watching the thunder and lightning and I could see the swirling front of the storm.

It was moving slowly, but then it started to get a bit faster in the middle and the clouds came down and formed a funnel. It was coming down lower and lower.''

Southbridge farmer Justine Menzies had lost a number of trees after what she believed was a tornado.

"I was in the house when it happened. It was like a roar, I've never heard wind like it."

Menzies said between 15 and 20 trees had come down from their property onto Main Rakaia Rd. She had spoken to motorists stopped by the felled trees who saw the twister.

"It was definitely a tornado."

STORM FELLS TREES

Hail and strong winds are causing havoc across Canterbury with fallen trees sparking a fire in the small town of Southbridge.

A Christchurch police spokesman said about three orfour trees had fallen onto the power lines at Southbridge sparking a fire in a paddock.

The storm had only just hit the city and was expected to move north this evening.

STORM A 'SUPERCELL"

Earlier today, the MetService issued a severe thunderstorm warning for parts of Canterbury with parts of the region set to be pelted with large, damaging hail and torrential rain.

MetService meteorologist Chris Noble said the storm was formed off the coast of Timaru and made its way north in the late afternoon hitting Christchurch just after 5pm.

The storm was "technically classed as a supercell" and had caused heavy rail, large hail stones and small tornadoes.

"When a thunderstorm grows and exhibits those severe characteristics, it's a supercell," he said.

While the tornado reported near Southbridge had not shown on the Met Service's radar, Noble did not doubt its existence.

"When they are formed over water, we call them water spouts...and if it's formed from a cloud but doesn't touch the ground, it's a funnel," he said.

They could sometimes cause damage but were "nothing like what the midwest experiences in the USA".

However, the weather would change overnight and tomorrow the region could expect fine conditions with northeasterlies.

RESIDENTS WARNED

MetService said in a statement this afternoon that its radar had detected thunderstorms near the mouth of the Ashburton River about 3.15pm.

The severe thunderstorms were moving north east and were expected to bring "very heavy rain and large hail" to Ashburton, Selwyn and Christchurch.

"Very heavy rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous," the statement said.

This morning, MetService forecaster John Crouch said parts of Canterbury could be affected by ''large, damaging hail and squally winds'' gusting up to 100 kmh.

Forecaster said some hail stones could be bigger than 2 cm in diameter. It could cause damage to crops and make driving conditions dangerous, Crouch said.

He advised people to move their vehicles undercover to avoid damage like broken windscreens.

People should to ''take care'' if they saw ''big, dark looking'' storm clouds approaching from the south or south-west.

Damaging hail storms usually affected parts of Canterbury two or three times each summer.

''An upper cold trough is expected to move across the South Island today making the atmosphere very unstable over southern New Zealand,'' Met Service's website says.

In December, Mid-Canterbury experienced hail stones up to 3cm in diameter that damaged crops and smashed windows in the Mayfield area.

The Ministry of Civil Defence and Emergency Management advises that as storms approach you should:

- Take shelter, preferably indoors away from windows;

- Avoid sheltering under trees, if outside;

- Move cars under cover or away from trees;

- Secure any loose objects around your property;

- Check that drains and gutters are clear;

- Be ready to slow down or stop, if driving.

During and after the storm, you should also:

- Beware of fallen trees and power lines;

- Avoid streams and drains as you may be swept away in flash flooding.