Lanes on Auckland Harbour Bridge are likely to close today as MetService warns of strong winds in much of the country.

A wintry blast has hit the country, with snow covering parts of Southland and Otago, and in the North Island, the Desert Road was closed overnight because of ice.

Waka Kotahi issued amber and red alerts for the Auckland Harbour Bridge.

Gusts of 75 to 80km/h were forecast through to 7am.

A red alert was in place from midday to 9pm with wind gusts of 90-100 km/h forecast and possible gusts of 100-110 km/h.

If those alert levels were triggered, all lanes on the bridge would be closed for most of the day, Waka Kotahi said.

Drivers of high-sided vehicles and motorcyclists are advised to avoid the Auckland Harbour Bridge and use the western ring route on state highways 16 and 18.

Meanwhile, Aucklanders were also warned to expect ongoing train disruptions today.

Auckland Transport said an electrical fault forced the cancellation of all Eastern Line services while Southern Line services are being reduced to every 20 minutes.