There is disbelief at the widespread damage caused by a tornado in Greymouth this afternoon.

Several people are understood to have been injured after the twister ripped through the West Coast town around 1pm.

It ripped roofs off buildings, and completely destroyed several businesses.

Grey District Mayor Tony Kokshoorn said he could not believe that no-one had been killed. He said you have to see the devastation to believe it.

Mr Kokshoorn said the roof of Dispatch Engineering -- one of the biggest buildings in town -- had lifted and came flying through the air towards him as he drove away from council chambers. 

He said he dived into the back seat of the car and hung on while it smashed into the vehicle. 

"There's a lot of destruction -- the tornado's come in from the sea and it's gone right through."

Local man Donny King said everyone was walking around, stunned at the damage.

He said there were sheets of roofing iron lying around and cars have been smashed. 

Chief Fire Officer Alan McEnaney is stationed in Blaketown, where he said there has been extensive damage. 

Mr McEnaney told Newstalk ZB's Danny Watson that 12 to 14 houses had been completely demolished along with a number of businesses. 

However he said the good news is that at this stage only one person has been sent to hospital. 

He said all the places where people may have been who might have needed assistance have been checked, and they believe everyone has been accounted for. 

But the same could not be said for the buildings. 

The Grey District Council is not, however, planning to declare a civil defence emergency. 

Mr Kokshoorn said there appeared to be no serious injuries or loss of life, despite the incredible damage. 

He said emergency services had worked very hard to take control of the situation. 

However, he said the clean up was going to cost millions of dollars. 

Staff at the Port of Greymouth reported considerable damage in the port area.

Only one wall was left standing at Allan Devine Engineering, a truck had been blown into the lagoon, a car was missing, containers were "spun around" and windows had been blown out of a bus company's vehicles.

Debris had been blown into nearby hills.

A larger vessel in the tornado's path appeared to have escaped damage, and it missed boats in the lagoon were not in the tornado's path.

Staff said the damage was worse than that caused by the tornado in 2003

Black clouds "billowing" into the sky was the first sign of a tornado that ripped through Tainui St said local resident Jessie Deck who saw the devastation.

The tornado caused extensive damage to buildings in the street including Dispatch and Garlic engineering company, and a Civic Video store.

Ms Deck said the walls of the engineering company were ripped off, and the building was destroyed.

It also affected surrounding suburbs, said Ms Deck.

"I was very scared. I heard this really large noise, and I looked up and black clouds were billowing up and huge bits of iron were flying through the air," she told NZPA today.

"The damage is unreal."

Ms Deck said she also saw a truck upside down in a lagoon.

The tornado caused havoc in just a few seconds, but the damage it caused was "mind-boggling", Ms Deck said.

A staff member at the Caltex service station in Tainui St, Claire Murphy-Klempel, said a nearby video shop had been "destroyed".

She said part of the service station forecourt was blown off, windows blown out, cars damaged, a fence demolished and branches stripped off a pohutukawa tree.

"It was huge -- massive -- I could see the iron flying around."

Around 100 residents of Kowhai Manor retirement home were evacuated.

St John's Ambulance in Greymouth said they had had two calls for people with minor injuries.

No details of the injuries were immediately available.

Meanwhile, the AA reported that high winds were hitting State Highway 73 between Arthur's Pass and Springfield -- a major route to the West Coast -- advising drivers of high-sided vehicles to take extreme care.

In June 2003, about 20 businesses were damaged when a tornado cut a swathe through downtown Greymouth and caused damage costing more than $300,000.

One building, in Albert St, was suffered such severe structural damage in the June 16, 2003 tornado that it was made unusable with the winds causing the back wall of the business to bow.

The 2003 tornado swept in off the Tasman Sea at about 9.45am, wreaking havoc on the western end of the central business district, snapping concrete power poles and knocking over street lights.

A similar tornado ripped through Greymouth in the early hours of March 28 2001, wrecking houses.

No one was injured then, but glass shattered and iron buckled in some homes.