UPDATED 5.15PM 

After thick fog caused disruption to Auckland today, there's now a warning it's set to return tonight.

WeatherWatch.co.nz has issued a fog advisory for the upper North Island overnight, and warns that fog patches are possible in other sheltered parts of New Zealand.

The site warns that heavy fog may still be sticking around by Sunday morning at some New Zealand airports.

Travellers should check airline and airport websites for updates.

Fog is also looking likely in Waikato overnight.

WeatherWatch.co.nz said the fog was being caused by a strong high crossing the country, and currently centred over New Zealand.

But there's some relief in sight, as northerly quarter winds are expected to develop across Sunday, and hopefuly end the foggy conditions in most places.

Today's fog caused delays and cancellations for 119 flights at Auckland Airport, including three international flights.

The poor visibility left 51 domestic flights were delayed, 64 domestic flights cancelled and one flight diverted to Wellington airport.

Three international flights were diverted to Wellington, from Nadi, Brisbane and Melbourne.