Ed Sheeran has been welcomed to his first sell out NZ concert by a rousing powhiri.

A 25-strong group representing different iwi greeted Ed Sheeran at Mt Smart Stadium this afternoon ahead of tonight's concert for a 47,000-strong capacity crowd.

The Maori welcome was at his request after he realised he'd not experienced one before.

However, it is the rain which is causing problems for concert organisers tonight.

Sheeran is refusing to let the rain dampen spirits tonight, saying "it sounds weird but some of the best shows are when it's raining".

MetService is forecasting showers and possible thunderstorms during the show tonight.

The popstar is on stage at Mt Smart this evening at 8:45, with the wild weather forcing changes to the screens and stage area for audience safety.

MetService meteorologist Brian Mercer says a number of areas from Northland to north Hamilton, including the concert arena, are at risk of receiving a downpour.

"We could get rainfall of up to 25-40mm if one of those severe thunderstorms forms."

Traffic on the Southern Motorway from Ellerslie to Greenlane is particularly heavy.

NZTA traffic maps showed an average speed of about 32km/h down this stretch.

The Mt Wellington Highway by Sylvia Park is moving very slowly also, along with Ti Rakau Drive by Pakuranga Intermediate.

Some roads are closed around Mt Smart stadium.

Frontier Touring released a statement saying adjustments have been made to the staging and screens to ensure the safety of the audience.

Fans have been told to take a poncho because umbrellas are banned from the stadium.

Nearby businesses and residents are cashing in on the concert, with some charging $20 to park on their properties.