Singer Leona Lewis kicks off Radio 1's Hackney Weekend
Leona Lewis has taken to the stage at BBC Radio 1's Hackney Weekend at Hackney Marshes in east London.
The singer is the first artist to play on the main stage which will also see performances from Ed Sheeran and headliner Jay-Z.
Earlier the music began on the outer 1Xtra and In New Music We Trust stages as well as the Dance Arena.
N-Dubz star Dappy and newcomer Jessie Ware were the first acts to perform at the event.
British singer Rita Ora and Canadian dance act Deadmau5 have also been on stage.
Leona Lewis was introduced by BBC Radio 1Xtra DJ Trevor Nelson who said: "[She is] the most famous singer to have ever come out of Hackney."
The singer opened the event with a cover of Diddy Dirty Money's song Coming Home featuring a guest performance from rapper Wretch 32.
Fans have been making their way on site since the gates opened at 10.30am with some people camping out since the early hours to get to the front.
Around 50,000 people are attending the first day of the free two-day event which is part of the UK-wide London 2012 Festival.
They have had to go through metal detectors and had their bags searched before getting into the site.
Hackney was one of the areas of London at the centre of last year's riots and is known to have gang problems.
Before the show ticketholders were contacted and advised to allow at least two hours to get into the arena.
Radio 1 reported queues of around 35 minutes just after midday.
Louisa Danquah, 16, from Hackney was one of the fans to come through the security checks.
She said: "You can't be too careful. For my safety, for everyone's safety it's best. I don't mind at all. It was quick and efficient."
Temi Tioo, 17, Bromley, south London, said: "I was in the queue for an hour but we came early. I think the scanners are important because you never know what kind of trouble wants to bring. Better to be safe than sorry. It's the right procedure."
Chief Superintendent Richard Woolford from the Metropolitan Police said they were "confident" and "happy" with the security and safety planning around the event.
Sade Antoinette, 20, from Hackney was at the front of the queue and said: "We've been here since 6am. We didn't didn't sleep. It's so exciting."
Shanicee Amoani, 16, from Stoke Newington, London, said: "I can't wait to see Jay-Z and Nicki Minaj. Hopefully we'll be at the front. I'm sure it'll be a great day and even if it does rain, it'll still be good."
Jay-Z is headlining the line-up which also features Ed Sheeran and Nicki Minaj.
It is the biggest live event organised by BBC Radio 1 in its 44-year history and more than twice the size of the network's annual Big Weekend.
More than 250,000 people applied for tickets when registration opened in February.
BBC Radio 1 and 1Xtra's controller Ben Cooper said: "Hackney is the perfect fit for us - an Olympic borough with a vibrant music scene and a large young population, many of whom can often be overlooked and disengaged, so exactly the people that we wanted to reach and inspire."
The weather forecast for Saturday is dry and breezy throughout the day, with some rain expected for late in the evening.
Artists taking to the stage on Saturday include Nicki Minaj, Kasabian, Ed Sheeran, Jack White, will.i.am, Emeli Sande, Calvin Harris and Swedish House Mafia.
More than 100 artists will perform across six stages throughout the weekend.
Project Hackney, a group from a pupil referral unit in Newham, east London, were the first act to perform on the Introducing Stage.
Sunday's line-up features headliner Rihanna along with performances from Florence and the Machine, Tinie Tempah, Jessie J, Plan B, David Guetta and Lana Del Rey.
Coverage of Hackney Weekend will be on BBC Three, BBC Radio 1, BBC Radio 1Xtra and online.