Roads have been closed, roofs lifted from houses and Dunedin is bracing for potential flooding as ex-cyclone Fehi makes landfall in the South Island.

A number of roads have been closed in the Nelson and Tasman areas and on the West Coast because of the weather, say police.

Nelson's Rocks Rd, a section of State Highway 6 that runs along the coast, has been closed.

Schools in South Dunedin have closed early and the Dunedin City Council is preparing for slips, flooding and road closures as the city is battered by ex-Cyclone Fehi.

Dunedin - which experienced the hottest temperature of close to 35C in New Zealand yesterday - is now expected to bear more of the brunt of the storm than initially expected, but heavy rain and wind is expected across Otago and MetService has upgraded its heavy rain warning for the region, with more now expected to fall.

Schools in South Dunedin, including Bathgate Park and Kings High School, are closing early this afternoon due to concerns about flooding.

Civil Defence controller Sandy Graham says the city's emergency operations centre has been open since it began raining on Thursday morning.

More than 60mm of rain is forecast between midday and 4pm. It was a significant amount which had the potential to cause flooding, slips and disrupt traffic, she said.

Meanwhile, falling trees have closed several roads in Takaka, Ruby Bay and Central Rd South in Tasman.

Police are recommending that drivers take extreme care on the Coastal Highway between Greymouth and Westport as a number of trees have come down.

"The weather is making driving conditions extremely difficult and we're urging people to stay off the roads unless travel is absolutely necessary.

"If you do need to travel, please drive to the conditions – watch your speed and following distances," police say.

The main centre of ex-cyclone #Fehi is now making landfall on the West Coast/starting to track into the South Island. Flooding rains possible and damaging winds only now starting to push in - peaking across today: pic.twitter.com/uJjjBr1fFX

— WeatherWatch.co.nz (@WeatherWatchNZ) January 31, 2018

More than 145mm of rain has fallen in Milford Sound over the past 18 hours.

Ex-cyclone Fehi is between Franz Josef and Haast - and is tracking southeast.

Meteorologist Tui McInnes says Franz Josef has also taken a drenching from 125mm falling over the same period.

McInnes says the most notable weather change within the next two hours will be strong winds in the Canterbury High Country and Canterbury Plains.

Fire and Emergency southern communications shift manager Andrew Norris said a fire crew helped at a property in Westport where roofing had come loose in strong winds.

Dunedin City Council is warning residents of an increased risk of flooding and is ramping up preparations before heavier rain this afternoon.

By 9am about 20mm of rain had fallen. Another 60mm is expected between midday and 4pm.

"This is a significant amount of rain which has the potential to cause flooding issues, slips and disruption to traffic," the council's Civil Defence controller Sandy Graham says.

"Staff and contractors, and Civil Defence personnel are doing all they can to ensure the city is prepared for the anticipated downpour."

The areas most likely to be affected by flooding are low-lying areas such as South Dunedin and Mosgiel. Heavy rain may also cause localised issues for the hill suburbs.

This morning there was some minor surface flooding in Portsmouth Drive, Marne St and Macandrew Bay.

However, there were no major roading or stormwater issues.

The council is monitoring the situation closely before heavier forecast rain this afternoon.

Staff and contractors have been working since 4am to make sure systems are clear and running well.

Dunedin Emergency Operations Centre opened at 9.30am to monitor and co-ordinate the situation.

Dunedin City Council advice:

• Some roads will be closed early, with detours available, if surface flooding becomes an issue. Keeping off roads with a lot of surface water means water is less likely to wash into properties.

• People concerned about rising water can pick up sandbags from the carpark behind St Clair Tennis Club, Victoria Rd and Mosgiel's Memorial Park carpark beside the stadium/Mosgiel Memorial Gymnasium.

• Slip sites and stormwater screens around the city are being checked, with no reported problems at this stage. The council will continue to monitor them.

• Check spoutings and drainage channels for blockages and clear them if necessary

• Lift items from the floor of basements prone to flooding. Be sure garden sprays and other chemicals won't be affected.

• Check stormwater grates near your house for blockages and keep them clear of leaves and other debris to avoid water building up and affecting your property.

In Ravensbourne, Dunedin, a crew had cut down a tree that fell onto some power lines. It did not cut the power.

Buller Civil Defence says the predicted severe winds have arrived: "Please remain vigilant and stay away from beaches and exposed areas."

Westport checking in. Just retrieved the top off of my chimney 😓 pic.twitter.com/MPMDmFznjN

— Hilary (@hilarymcam) January 31, 2018