Ariana Grande says she is "praying for London" ahead of the benefit concert for the Manchester terror attack victims.
The American star is due to return to the stage for the first time on Sunday night (Monday AEST) after suicide bomber Salman Abedi detonated a device, killing 22 people as they left her show at the Manchester Arena on May 22.
The One Love Manchester event will take place less than 24 hours after six people died in the London Bridge attack - the country's second terrorist outrage in less than two weeks.
Grande tweeted an emoji of a heart, and wrote: "Praying for London."
Other musicians including Justin Bieber, Katy Perry, Coldplay, Take That and Miley Cyrus are to join Grande for the Sunday night event.
Grande has visited victims of the attack at the Royal Manchester Children's Hospital ahead of the show, where she will also be joined by Robbie Williams, Little Mix, Usher, Pharrell Williams and One Direction star Niall Horan.
Proceeds from the concert will go towards the We Love Manchester Emergency Fund, set up by Manchester City Council in partnership with the British Red Cross, to support grieving families and victims of the bombing.
On Saturday, it was confirmed that the fund had reached STG7.2 million ($A12.5 million).
All Grande fans who attended the targeted gig were offered free passes to Sunday's benefit concert regardless of where they purchased their tickets.
More than 10,000 people applied for free tickets to the concert last week despite not attending the pop star's targeted gig.
Ticketmaster set aside tickets for the 14,200 people who were at the Manchester Arena concert, but more than 25,000 people applied to attend the event.
The STG40 tickets that went on sale for the show at the Old Trafford cricket ground were snapped up in less than 20 minutes.
Millions of people around the world will also be able to watch as the concert will be simulcast in more than 50 countries across five continents.
