MetService has lifted a red severe thunderstorm warning for Northland, but a storm watch is still in place over the wider Northland and Auckland regions.

MetService says its radar detected a line of severe thunderstorms moving northeast.

The thunderstorms are likely to be accompanied by very heavy rain, damaging wind gusts and hail, it said.

It warned that strong gusts can cause structural damage to trees and powerlines, and heavy rain could cause surface or flash flooding.

A thunderstorm watch is in place for Auckland and the rest of Northland.

A strong wind watch is also in place for Northland, Auckland including Great Barrier Island, and the Coromandel Peninsula.

MetService says the National Emergency Management Agency advises that as storms approach you should:

• Take shelter, preferably indoors away from windows;
• Avoid sheltering under trees, if outside;
• Get back to land, if outdoors on the water;
• Move cars under cover or away from trees;
• Secure any loose objects around your property;
• Check that drains and gutters are clear;
• Be ready to slow down or stop, if driving.
• During and after the storm, you should also:
• Beware of fallen trees and power lines;
• Avoid streams and drains as you may be swept away in flash flooding.

More than 400 households in the Far North are without power after thunderstorms passed through the region.

Electricity provider Top Energy says an outage is affecting Waima, Taheke and Otaua.

It estimates 433 customers have been without power since 8.45am.

Harbour Bridge warning

An area warning is in place for Auckland's Harbour Bridge due to strong winds.

Waka Kotahi warns that reduced speed limits and lane closures could be possible.

The bridge could be closed entirely if winds reach 90 kilometres per hour, it said.

The warning is in place until 8pm Saturday.

The transport agency is encouraging drivers of high-sided vehicles or motorcycles to consider using the Western Ring Route instead of the bridge.