As politicians from across the spectrum condemned the attack on Twitter, locals in Manchester also used social media to offer up accomodation.
Singer Ariana Grande, who had just finished performing in Manchester, northern England, when the blast took place, tweeted that she was "broken" by the attack.
"From the bottom of my heart, I am so, so sorry. I don't have words," the 23-year-old wrote on her verified @ArianaGrande account, which has more than 45 million followers.
As politicians from across the spectrum condemned the attack on Twitter, locals in Manchester also used social media to offer up accomodation and advice to those caught up in the chaos.
Here are some selected tweets.
US rapper Nicki Minaj (@NICKIMINAJ), who collaborated with Grande on recent hits "Bang Bang" and "Side to Side" tweeted: "My heart hurts for my sister, Ariana & every family affected by this tragic event in the U.K. Innocent lives lost. I'm so sorry to hear this."
US pop princess Taylor Swift (@taylorswift13), a friend of Grande, tweeted: "My thoughts, prayers and tears for all those affected by the Manchester tragedy tonight. I'm sending all my love."
Katy Perry (@katyperry), also a friend of Grande, tweeted: "Broken-hearted for the families tonight. Broken-hearted for Ari. Broken-hearted for the state of this world."
Up and coming American popstar Sabrina Carpenter (@SabrinaAnnLynn), who recently played in the northern English city with British pop rockers The Vamps, expressed her shock. "Just played Manchester.. crazy.. really don't have words. I'm so sorry. should be a safe place. :( Thinking of all those affected," she tweeted.
"Tearing up imagining innocent concert goers losing their lives," added US popstar Demi Lovato (@ddlovato). "Praying for everyone and all".
Grande's manager Scooter Braun, who also represents Justin Bieber, published a longer statement through his Twitter account (@scooterbraun).
"We mourn the lives of children and loved ones taken by this cowardly act," the sombre black and white picture statement read. "We ask all of you to hold the victims, their families, and all those affected in your hearts and prayers."
Politicians also took to social media to condemn the attack and send their condolences.
Jeremy Corbyn (@jeremycorbyn), leader of Britain's main opposition Labour Party tweeted: "Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services."
Andy Burnham, the newly elected Mayor of Manchester (@MayorofGM), added: "My heart goes out to families who have lost loved ones, my admiration to our brave emergency services. A terrible night for our great city"
London Mayor Sadiq Khan (@SadiqKhan) said: "London stands with Manchester -- our thoughts are with all those killed and injured tonight and our brave emergency services."
Nigel Farage (@Nigel_Farage), who led the anti-immigration UK Independence Party through Britain's divisive vote to leave the European Union tweeted: "Horrified at the bombing in Manchester. No doubt we will find out who the perpetrator is soon. My thoughts are with those affected."
Outside Britain, leaders also expressed solidarity. Steffen Seibert, spokesman for German Chancellor Angela Merkel, said: "Our thoughts + prayers are with the people in #Manchester affected by the blast. We mourn for the dead + hope the injured can recover fully."
Across Manchester itself, locals used Twitter to say their doors were open to those needing a bed for the night or simply a cup of tea, many using the hashtag #roomformanchester.
"We have a spare double bed and two sofas available if anybody needs a place tonight," tweeted @iamjesyrae.
53Two, an exhibition venue some 500 metres (yards) south of the blast site, said it would keep its doors open late.
"If you need somewhere to come grab a coffee and await news, head to the arches. We've got the kettle on!" they tweeted.
Mohammed Shafiq, who runs the Manchester based inter-faith group the Ramadhan Foundation, said taxi drivers were helping out stranded concert goers.
"Manchester taxis and cabs offering free rides home for people around #manchester Arena. One love," he tweeted @mshafiquk.