Ed Sheeran takes to stage and thanks rain-drenched fans for turning up

International superstar Ed Sheeran has opened his Auckland show with hit song Castle on the Hill.

After his first song the star took a moment to greet the sodden rain-drenched crowd.

"Hello Auckland, thank you for coming, thank you for braving the weather ... I hope you know the words otherwise it might be a long two hours."

In the minutes before his appearance the tension among the crowd had been palpable, as one of Sheeran's crew came on stage to test the sound.

They didn't have long to wait as the star bounded on stage a few minutes early and a whole two minutes earlier than scheduled.

He launched straight into the first song of his set strumming his guitar as clouds of blue-black smoke filled the screens behind him and the crowd got on their feet.

Mum just got annoyed at me cause I told her to mute the Kardashians on tv so I could listen to Ed Sheeran

— chrispy (@chrispytunafish) March 24, 2018

Forecasters earlier issued a thunderstorm watch for Auckland and warned fans on their way to the sell-out concert tonight to expect to get very wet.

Wild weather forced organisers to make changes due to safety concerns as earlier heavy rain and crashes brought traffic to a crawl across parts of the city today.

MetService meteorologist Brian Mercer said Sheeran concertgoers should expect to get very wet at the open-air Mt Smart Stadium.

The weather bureau has issued a thunderstorm watch for Auckland and Mercer said there was a moderate risk of thunderstorms across the city.

Gloomy at the venue, but that hasn't stopped the crowd. Photo / Rosemarie Baker

But the likelihood of one forming directly over the concert is fairly low, Mercer said.

The rain has already well and truly set in at Mt Smart.

Concertgoers have been posting photos and videos on social media showing torrential rain, with fans donning ponchos and raincoats in a bid to stay dry.

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Do stadiums they said....

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The supporting acts, Drax Project and Wellington folk duo Lost Bird are warming up the sea of coloured ponchos before Ed takes the stage.

But while it might be wet, the rain doesn't seem to be dampening too many spirits.

Congestion continues to cause headaches for motorists across the city.

Traffic around Balmoral is particularly slow, NZTA traffic maps indicate motorists are travelling 24km p/h in this area.

The St Lukes off ramp on the Western motorway is severely blocked and traffic is moving very slowly down the Ellerslie Panmure Highway.

One motorist said drivers appeared to be getting quite frustrated on the roads.

"It was really heavy going south toward Mt Smart stadium, people were queuing over intersections trying to get through the lights. People were obviously getting frustrated with the traffic," a motorist told the Herald.

South along the Southern Motorway towards Drury Interchange is particularly heavy. Photo/NZTA

Some roads are closed around Mt Smart stadium.

The weather has also meant Ed Sheeran concert organisers have been forced to make changes to the concert set-up.

Frontier Touring released a statement saying adverse weather conditions had impacted the production set-up for Auckland's three sell-out Sheeran shows.

"As a result, all three Auckland concerts will be affected with necessary adjustments made to the staging and screens to ensure the safety of the audience," the statement said.

Based on weather forecasts, Frontier Touring strongly advised fans to bring a poncho as umbrellas would not be allowed inside the venue; and to also allow extra time for travel to and from the venue.

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