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Ariana Grande has tweeted "thinking of you all" ahead of a day of remembrance to mark the first anniversary of the Manchester Arena attack.
Twenty-two people were killed and hundreds injured when a bomb was detonated at the end of one of her concerts on 22 May 2017.
Events include a service at Manchester Cathedral at 14:00 BST and a mass sing-along.
There will also be a national minute's silence at 14:30.
Grande, who staged the One Love concert in Manchester less than two weeks after the terror attack, said on Twitter: "I love you with all of me and am sending you all of the light and warmth I have to offer on this challenging day."
As the day unfolds people involved on the night have been giving their reaction to the anniversary.
Adam Lawler, 16, went to the concert with his friend Olivia Campbell-Hardy, who died in suicide bomber Salman Abedi's attack.
He was hit by shrapnel and suffered multiple injuries.
"I broke both my legs, lost seven teeth. I nearly lost my right eye. I regained vision in it thanks to the amazing doctors. I nearly lost my tongue," he said.
"If I could go back in time, I would change everything. But I can't, so what I'm going to do is I'm going to try and live my best life.
"We won't be beaten because we're Manchester."
Dan Hett, whose brother Martyn died in the attack, told the BBC the support he had received in the past 12 months had been "overwhelming".
He said he had been picked up off his feet and hugged by everyone from an "old lady in a supermarket to a six-foot biker".
Mr Hett, who is going to the service at Manchester Cathedral, said it "illustrates the support has come from every possible corner of Manchester".
He has tweeted a photograph of him with his brother, which is trending on social media along with #BeMoreMartyn.
Ella McGovern, 15, of Rossendale, Lancashire, suffered shrapnel wounds to her legs in the blast. She has since climbed Ben Nevis and a completed 10k run.
Her mother Louise McGovern said the anniversary would be "extremely emotional".
"I'm looking forward to being with everyone in Manchester - I think that will be very nice and positive.
"But I think I'm going to pack a few tissues."
Cath Hill, who is in the Manchester Survivors' Choir, a group made up of people who were at the arena on the night of the concert, said: "We have been through something really difficult but we do want to stand up and rise up and show everybody that we are carrying on and [going to] be positive.
"And we can make something positive out of this."
'I must've died 200 times in my nightmares'
Daren Buckley's life changed forever when the home-made device detonated metres away where he and his son were standing.
Yet the father of four's first instinct was not to flee, but to run to help the wounded.
He said: "The scenes in the foyer I can't describe. It was like a nightmare."
A year later he remains traumatised, saying: "I have flashbacks. I must've died 200 times in my nightmares."
Greater Manchester mayor Andy Burnham tweeted his support for everyone affected by the explosion.
"Today we come together, we remember each of the 22 people whose lives were taken."
Dan Smith, the second paramedic to arrive at the scene of the attack, said it was going to be a "difficult day", adding: "This date will never be the same again."
He said he got on with his job on the night of the attack and only realised the impact of the "massive attack" when he went home and saw it on TV.
Mr Smith said he did not want to dwell on the "devastation" or know anything about the man responsible for the attack, but focus on the "positives" from that night of how many lives were saved and the amazing response from the Manchester community and beyond.
Celebrities have paid tribute to the victims of the attack on social media.
Manchester-born actress and Strictly Come Dancing star Gemma Atkinson posted a picture on Instagram of the Manchester bee symbol with the words: "Stay strong our kid."
Stars of Manchester soap Coronation Street also paid tribute, including Lucy Fallon and Daniel Brocklebank.
Brocklebank, who plays vicar Billy Mayhew in the ITV soap, tweeted that his "love & thoughts" were with "those we lost a year ago".
Fallon, who plays Bethany Platt, tweeted: "Because this is a place where we stand strong together, with a smile on our face, greater Manchester forever."
Comedian John Bishop also tweeted: "Thoughts and prayers today are with all those who were affected by events in Manchester a year ago."
How can people watch the events?
You can view special "Manchester Arena: One Year On" programmes live on the BBC news channel or via the BBC News website at these times:
13:45 BST to 15:15 BST: Special coverage of the National Service of Commemoration, on the first anniversary of the Manchester Arena attack, including a minute's silence at 14:30 BST.
19:00 BST to 21:00 BST: Special coverage of the "Manchester Together" commemoration event.