Online reaction to the suspected terror attack on a pop concert that killed at least 19 people has been swift.

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.

Here are some selected tweets from the worlds of entertainment and politics.

US rapper Nicki Minaj (@NICKIMINAJ), who collaborated on the hit "Bang Bang" with Grande 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."

Jeremy Corbyn (@jeremycorbyn), leader of the 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) tweeted: "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."