Harry Styles fans begin long wait inside Auckland's Mt Smart hours before Love on Tour show

Harry Styles fever has hit Auckland with the pop star being spotted at the Viaduct Harbour and fans amassing at Auckland's Mt Smart Stadium some 12 hours before he is due to take the stage.

The pop star is in Aotearoa for one show only on Tuesday night as part of his Love on Tour.

On Monday evening footage was posted online of Styles at the Auckland CBD's waterfront area meeting fans - one of whom asked to get a photo with the former One Direction star.

"Do you mind if we don't?" he replied.

When the fan didn't push him and said they were attending the concert, Styles said: "Nice to meet you guys, hope you have a nice day… enjoy the show!"

Some fans from around the globe have headed to Auckland for the concert, with one on social media posting from Australia that she was on her way to the show. Styles has just wrapped up a series of concerts across the Tasman with gigs seeing him doing a shoey on stage and wearing a Bunnings hat.

"He's such a gorgeous young man and his music is so fantastic. He's got a sort of charisma about him and I always say he's an evolved young man - and I like that," superfan Sharon from Wellington told AM.

On Monday, some 24 hours before Styles was even in the country, people were posting on social media about how they were already in the queue at Mt Smart to buy merchandise from the show.

"The things we do," one posted, with a picture of the mainly young female fans queueing.

But on Tuesday morning just after 8.25am, one fan posted from inside Mt Smart Stadium, 12 hours before Styles was thought to be performing.

"I'm in the venue now Harry Styles," they wrote.

Other fans told AM they would be heading to the venue early to "get in line for the T-shirts", with merchandise stands at the stadium opening at 10am.

Around 40,000 fans are expected at the concert tonight in Auckland and there are warnings for concertgoers to "plan ahead" to avoid traffic mayhem.

Auckland Transport said the city's travel networks are already under strain due to more travellers than usual during what's been dubbed "March Madness".

To make matters worse, ongoing KiwiRail rail closures on the Southern and Onehunga lines in Auckland mean even more disruption before and after the concert.

"We have put a range of transport options in place to make sure everyone gets to the concert and home safely. This includes free transport on the day for ticketholders across all regular timetabled bus and train services; and limited dedicated Special Event Bus Services," Richard Harrison, AT's Manager of Metro Optimisation said in a statement.

"Rideshare, taxi, and private vehicle drop-off locations are available within walking distance of the stadium along with park-and-ride and park-and-walk options."

Meanwhile, Styles has been told he will have to complete the New Zealand Census while here. 

March 7 is census night.

Asked on Twitter if he was required to take part, a spokesperson from the census replied that there's no special exemptions for anyone.

"Everyone who is in Aotearoa New Zealand on census night (Tuesday, March 7), needs to be counted in the census," the spokesperson said.

"This includes tourists, visitors, and former members of One Direction."