The show will go on in Manchester today, despite the terror attack in London on Saturday.
Grande's manager Scooter Braun appeared on stage wearing a black One Love Manchester baseball cap with the pink logo for the concert on the front to introduce the singer on her return to the city less than two weeks after she said she was "broken" by the attack.
A Cowes theatre is hosting a showing of the Manchester benefit concert tonight (Sunday), starring Ariana Grande, Coldplay, Katy Perry and Justin Bieber, among others.
"I don't feel or smell or hear or see any fear in this building".
On Friday, Grande visited some of her injured fans at the Royal Manchester Children's Hospital.
Manchester police said in a statement Sunday that there would be "additional security" in place at the event and asked people not to bring bags in order to speed up entry as "everyone will be searched".More news: Terrorism one of the biggest challenges world facing today, says PM
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"Manchester, your bravery is our hope", Braun said. After pedestrians were hit, officials say that three men armed with knives fled the scene and began attacking people at local restaurants and bars around the nearby Borough Market.
All Grande fans who attended the gig on May 22 were offered free passes to the benefit concert.
Describing the "emotional" atmosphere at Old Trafford, Sky's Entertainment Correspondent Katie Spencer said: "It's turning into a real celebration of community spirit and people coming together".
The concert will feature Ariana Grande, the American singer whose show was targeted by bomber Salman Abedi a few weeks ago, leaving 22 dead and 116 injured.
The large crowd fell silent at the start of the concert to remember those who were killed and injured in both Manchester and London. The show is broadcasting across the globe and proceeds will go to an emergency fund set up by the city of Manchester and the British Red Cross. "We must not be afraid, and in tribute to all those affected here and around the world, we will bring our voices together and sing loudly", he continued.
May said that "following updates from police and security officials, I can confirm that the awful incident in London is being treated as a potential act of terrorism". "So that is what it will continue to do for us".