Severe gales, heavy rain and snow are forecast for parts of Southland tonight.

The MetService has issued weather warnings as a low and its associated fronts move onto the South Island from the Tasman Sea.

"This weather system is forecast to bring heavy rain and strong winds to many parts of central and southern New Zealand, and possible heavy snow to southern Fiordland," a MetService meteorologist says.

A 'strong wind warning' is in place for Southland, Fiordland and Otago until 11pm tonight, with northwest gales forecast to be severe at times, with gusts reaching 120 km/h in exposed places.

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"Strong wind gusts could damage trees, powerlines and unsecured structures. Driving may be hazardous, especially for high-sided vehicles and motorcycles."

Fiordland is expected to bear the brunt of the front, with also a heavy rain warning and heavy snowfall watch in place.

Periods of heavy rain, at rates of 10 to 20 millimetres per hour, are forecast between 4pm today and 3am tomorrow, which may cause rivers and streams to rise rapidly.

Snow is forecast to fall to 400 metres overnight Monday, from 11pm to 11am, in Fiordland south of Te Anau. Snow accumulations may approach warning criteria 500m and above.

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And that means there's a road snowfall warning in place for SH94, the Milford Road, where 1 to 2cm may settle, particularly tomorrow.

The low should move away to southeast early Tuesday while the associated fronts, followed by a cold southwest change, move northeast across New Zealand.

But a second colder southwest change is expected to spread up the country from late Tuesday into Wednesday bringing snow to even lower levels.

"Warning amounts of snow is not expected with this second cold change at this stage," the meteorologist says.

"However, snowfall is expected to affect many South Island roads and passes and may cause stress to livestock. People are advised to keep up to date with the latest forecasts."

Check the MetService website for updates.