Motorists using the Auckland Harbour Bridge are being warned of delays due to strong wind gusts, with an amber alert in place until late morning.

Severe winds forced the closure of lanes to two in each direction for a short time on Wednesday morning.

Wind gusts on the bridge were expected to reach 70 to 85km/h, as strong southwesterlies hit the city.

Drivers of high-sided vehicles and motorcyclists were advised to avoid the bridge and use the western ring route on State Highways 16 and 18.

The amber alert was in place until 11am.

Motorists were urged to drive to the conditions, look out for the electronic message boards which will indicate lane closures and reduced speeds, and stay within their lane while travelling across the bridge.

In the central North Island, snow has closed State Highway 1 from Taihape to Rangipo, and motorists are advised to delay travel or use the alternative route along SH49, SH4, SH47 and SH46.

A MetService strong wind watch is in place for Northland south of Kawakawa, Auckland including Great Barrier Island, Coromandel Peninsula, Waikato north of Huntly and coastal areas from Tokomaru Bay to Wairoa.

Southwesterly winds are forecast for Dunedin, North Otago, Clutha and Southland south of Lumsden including Stewart Island on Thursday and could approach severe gale force in exposed places, MetService said.