Two streets in Hokitika have been hit by serious flooding as rain lashes the West Coast and much of Canterbury.

Westland District Council has reported "serious flooding in Sewell and Sale St, Hokitika, at the moment".

"Our contractors have every available person working on this at present. We're looking at additional pumping at the pump station to also help with this," the council said on Facebook.

"Please take care if driving. If you become aware of flooding in any other areas of Hokitika that need urgent attention please phone us on 756-9010. Many thanks."

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Update (2.38pm) Serious flooding in Sewell and Sale Street, Hokitika at the moment. Our contractors have every...

Posted by Westland District Council on Wednesday, 10 January 2018

MetService forecaster Cameron Coutts said Hokitika has recorded 40.8mm of rain in the past hour, bringing the total rainfall to 92.4mm in the past six hours.

"There have been downpours in and around the Greymouth area which has caused some flooding - about 145mm in the last 24 hours, of which 60mm fell in two hours from 9am to 11am," he said.

"It's still raining there but a little bit lighter."

Grey District Council listed six roads on Facebook which remain closed, though others have been opened.

UPDATE: 4.15pm, Thursday 11 Jan 2018 More heavy rain is expected for the rest of the afternoon and potentially longer....

Posted by Grey District Council on Wednesday, 10 January 2018

"More heavy rain is expected for the rest of the afternoon and potentially longer. If your property is at risk of flooding, please put your belongings up high," it told residents.

The NZ Transport Agency has reopened State Highway 7 between Greymouth and Reefton, but warns that there is still surface water on the road.

Greymouth was braced for the possibility of further flooding later today after this morning's continuous downpour caused widespread flooding, inundating several homes and business premises and prompting evacuations.

About 145mm fell overnight in Greymouth.

By 11.30am Fire and Emergency NZ had fielded 29 calls and the Montessori preschool and several residences in Alexander Street and upper High Street were evacuated.

A close eye was being kept on Sawyers Creek, which was reported to be at its highest flood level since the devastating floods of the 1970s that inundated much of the eastern suburbs.

By midday floodwaters were draining away quickly, but with a further 100mm of rain forecast this afternoon the Grey District Council was taking precautions by filling sandbags.

Greymouth Volunteer Fire Brigade fire chief Lee Swinburn said the calls began about 9am, when the rain intensified into very heavy bursts.

All outlying brigades including Brunner, Cobden and Runanga were called in to help.

"Our resources are stretched but we're handling it," Swinburn said at 11.40am.

"Obviously it's a short burst. We've had flooding like this previously -- short local bursts. It hasn't affected downtown as much."

The most affected areas were upper High Street and Alexander, Shakespeare and Lydia streets, as well as the Main South Road towards South Beach.

"Water has entered several properties, especially on the Alexander Street end," Mr Swinburn said.

"We are still pumping upper High Street with water drainage issues there. Water at the moment is receding and pumps are working but we are prepared for this afternoon because there's meant to be (more) heavy rain."

The public was responding well to police and council staff and there was "a good effort" by residents to clear stormwater drains, in particular.

"Everyone seems to be patient and aware of what's going on," he said.

Council assets and engineering manager Mel Sutherland said Sawyers Creek was the highest seen in decades.

"It the worst the current staff have seen."

The West Coast Regional Council had been notified and staff were keeping a wary eye on it this afternoon.

Vegetation had been cleared along the creek just prior to Christmas, Sutherland said.

However, it has decided to close a welfare centre that was opened this morning at the Westland Recreation Centre because no one has needed it.

Wellington Airport has reported flight disruptions.

Marketing manager Renee Carter said fog affected some flights to and from Wellington and other flights were delayed or cancelled due to weather conditions in other parts of New Zealand.

"Fiji Airways flight FJ 461 arriving into Wellington was diverted to Auckland earlier this afternoon," she said.

"Weather conditions have since improved and flights are continuing to land and depart however low cloud is forecast to remain for most of the afternoon.

"Travellers are requested to check any flight status either with their airline or the Wellington Airport website at www.wellingtonairport.co.nz."

The co-owner of Golden Bay Air which operates between Takaka and Wellington, Lisa Sheppard, said a flight to Wellington this morning was delayed by the fog in the capital but was now flying.