Music fans have said they had to attend the Manchester benefit concert to show they were determined to “stay strong and carry on”, despite recent attacks.
Around 50,000 people are at the concert, which comes 13 days after a bombing at an Ariana Grande show.
Grande has performed along with Take That, Robbie Williams and Coldplay.
“It’s quite emotional for us because it was quite a terrifying ordeal,” said Nicola Brownbill, who was at the original concert with her daughter.
“But we’re going to make the most of it and it’s a lovely atmosphere here today.”
Mrs Brownbill and daughter Hannah, 13, said they felt they had to attend to “support the people who weren’t so lucky as us”.
Mrs Brownbill said: “It was a really difficult decision, even as late as this morning, after last night’s event [in London]. We were questioning ourselves.
“But you’ve got to carry on. That’s what life is. I had more reservations than my daughter – I feel that I can’t stop her from living the life she wants to live.”
Around 50,000 people are attending the concert at Old Trafford cricket ground – including 14,000 who were at the original Ariana Grande show at Manchester Arena on 22 May.
Earlier on Sunday, Grande’s manager said the One Love Manchester concert would “go ahead with greater purpose” following the attack in London on Saturday.
Scooter Braun tweeted that “all artists involved have been unwavering in their support this morning and are determined to carry on with the show”.
Police said additional security is in place, with armed officers stationed around the ground.
Andrea Noon, also from north Wales, had been queuing since 1030 BST.
She said she had second thoughts about coming following the London attack. “After last’s night’s incident yes I did and part of me still is inside pretty scared,” she said.
“Obviously it’s always at the back of your head, what could happen. But we have to show them. We have to stay strong and carry on.”
Kira Donovan from Huddersfield, who was was at the original concert, said she wanted to attend to remember “all the true Ariana fans” who were at that show.
Her mum Amy added that they wanted to “celebrate, looking forwards, with the spirit of Manchester and all the fans” – but said she was worried about attending.
She said: “It was all right at the time of booking it but as it got nearer I was getting more and more anxious, and as we came in on the tram it did bring it all back a bit, that night.
“I knew it was going to be emotional but I didn’t expect it to hit me quite as hard as [it did] when we got nearer.”
The concert will raise money for those affected by the suicide bombing at the end of Ariana Grande’s performance at the Manchester Arena.
Twenty-two people were killed, including children and teenagers who saw the show as well as parents arriving at the arena to pick them up at the end of the night.
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Grande said she wanted to return to the “incredibly brave city” to spend time with her fans and to “honour and raise money for the victims and their families”.
Grande tweeted after the incident in the capital that she was “praying for London”.