Snow and ice are affecting and closing a number of southern highways on Thursday, while flooding in other areas mean drivers must take care, NZTA says.

Meanwhile a heavy snow dump and concerns about ice have left Tekapo cut off to traffic. State Highway 8 is closed until further notice.

MetService has issued a watch for heavy rain and snow in Westand, North Otago and Canterbury, which indicated rainfall accumulations could exceed 50mm in some parts.

Meteorologist April Clark said ''quite a broad trough'' was expected to push on to Canterbury on Thursday morning.

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''It's not an onshore flow, so it's got to come all the way over the ranges,'' she said.

While Otago could expect low temperatures and a few showers today, North Otago and Canterbury would get more persistent rain from late morning.

Heavy rainfall had been forecast for Westland, south of Otira, where up to 60mm was expected about the ranges and up to 30mm near the coast until about midday on Thursday on top of what has already fallen.

Snow was falling across inland Canterbury.

Clark said heavy snow also expected for the Lewis, Arthur's, Porters and Lindis Passes and the Milford Road, and could all be affected for a time.

State Highway 8 (Tekapo to Fairlie and Twizel to Tekapo) were closed, as was State Highway 80 to Mount Cook National Park due to snow and ice. No detours were available.

NZTA said there was also ice and snow on State Highway 6 (Haast to Makarora) and if using the Lindis Pass (State Highway 8 Tarras to Omarama), chains must be carried.

Check highway conditions here

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Snow was forecast for the Queenstown and Central Otago areas. Drivers should also watch out for surface flooding and the risk of black ice forming if temperatures dropped, councils advised.

Road works were under way after recent flooding and this could cause delays.

State Highway 8 (Roxburgh to Raes Junction) and State Highway 85 (Omakau to Kyeburn) were affected by flooding and road users were advised to take care, NZTA said.

In the North Island, the MetService issued road snow warnings including the Desert Road and Rimutaka Hill Road. Up to 10cm of snow was expected to fall in the central plateau highway from midnight tonight until midnight Saturday.

Oamaru ready for any rain

Last Friday, Oamaru had its wettest day since daily rainfall records started in 1950 with a total of 161.2mm.

Waitaki Mayor Gary Kircher said yesterday that due to the saturated ground and the ongoing recovery work, Waitaki District Council staff were ''very mindful of how stretched resources might get if it does affect us greatly''.

Staff would make sure drains were clear to cope with any rain.

Niwa meteorologist Seth Carrier said ''the heaviest rainfall amounts'' would probably miss Otago entirely.

Niwa modelling showed South Otago could record under 10mm and in North Otago the amounts would be closer to 15mm to 25mm, which could still lead to localised flooding.

- Reporting by Hamish MacLean