From one Labour leader to another, Britain's Jeremy Corbyn has given Jacinda Ardern a good luck shout-out for this month's election.

He wishes her luck in footage that appeared online on Thursday morning.

"Jacinda, all the best in the election. Make sure you do it. For all of us," he said in the video posted by TVNZ presenter Jack Tame.

Labour's turnaround in the polls in New Zealand is reflective of a similar movement toward the left in Britain's elections earlier this year.

In the snap election called by Conservative leader and Prime Minister Theresa May, the UK Labour Party managed to gain 30 seats, its highest percentage in nearly two decades.

Current polls in New Zealand put the difference between Labour and National at its closest in a decade.