The Prime Minister was among hundreds of air passengers who had travel plans disrupted by fog yesterday. Morning flights were cancelled around the country and airlines spent the rest of the day battling to get their schedules back on track.

About 25 flights from Auckland were cancelled and several were unable to land before the fog cleared about 11am.

The adverse conditions caused more problems for embattled carrier Jetstar whose planes lacked the technology to get in and out of fog-bound Queenstown.

John Key was among Jetstar passengers stranded in Queenstown - until he was flown back to Auckland by Air New Zealand.

Wellington students Edward Warren and Will Mahon-Heap missed a friend's farewell party as a result. "It's bloody useless," said Warren. "They've made a real cock-up of things."

Passengers also claimed staff directed them to an 0800 number that didn't appear to be staffed.

Jetstar staff at Wellington referred media inquiries to a spokesman in Australia, who was unavailable.

The fog marked the end of an unusually long cold snap for Auckland that saw overnight lows plunging to minus 1C last week, colder than snowy Dunedin.

Weatherwatch head weather analyst Philip Duncan predicted overnight temperatures would rise by an average 4C this week.

The price for many may be heavy rain today and tomorrow, as a deepening low moves south across the North Island.