The Greater Manchester Police said in a statement, "There are a number of confirmed fatalities and others injured". Earlier in the day, BBC had reported the arrest of a 23-year old man in connection with the blast in Machester.
There were reports on Tuesday morning that police had closed London's Victoria Coach Station and surrounding streets, after a suspect package was found in the area. Twitter and Facebook were filled with appeals for the missing.
Witnesses said the blast scattered bolts and other bits of metal, indicating the bomb may have contained shrapnel meant to maximize injuries and deaths.
In other messages, taxi drivers and Manchester residents offered to ferry those who needed to leave the city for free, while the hashtag #RoomForManchester was being used to offer free bedrooms and sofas for anyone stuck in the city.
Grande, who had just left the stage, was unhurt, taking to Twitter to say: "From the bottom of my heart, I am so, so sorry". The police believe they know the man's identity.but can not confirm his name. Walker, who is from the northern city of Leeds, said she had a stomach wound and possibly a broken leg.
She added: "Across the United Kingdom we are today grieving for the people of Manchester".
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He urged Muslim leaders to play a more proactive role in combating extremism. Drive them out of your Holy Land. "Drive them out of your communities".
The explosion occurred during Grande's closing song, according to videos released by audience members. "It was very, very loud", she said, adding that her husband thought he had heard a second explosion. We just tried to get back in. trying to get the girls. "What should have been a superb evening is now just disgusting".
She and other candidates suspended campaigning for Britain's June 8 election after the blast.
Police said they believe a man carrying explosives acted as a lone attacker and died in the powerful blast that shook part of the cavernous Manchester Arena as concertgoers streamed out after the American pop star's last song.
Police cars, bomb-disposal units and 60 ambulances raced to the scene as the scale of the carnage became clear.
In March, a British-born convert to Islam plowed a vehicle into pedestrians on London's Westminster Bridge, killing four people, before stabbing to death a police officer who was on the grounds of parliament.
Concert attendee Majid Khan, 22, told The Guardian newspaper a bomb-like bang went off as people were exiting the 18,000-capacity venue, leading to a mass panic. "So many young attractive, innocent people living and enjoying their lives murdered by evil losers in life".
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London Mayor Sadiq Khan said London stands with Manchester after the "barbaric and sickening attack". "I don't have words". The Dangerous Woman Tour is the third concert tour by Grande and supports her third studio album, "Dangerous Woman".
"I know I speak for everyone in expressing my deepest sympathy to all who have been affected by this terrible event and especially to the families and friends of those who have died or were injured", she said. "Anyone seen my daughter Olivia Campbell", she wrote.
Fan groups around the world shared their support.
Scottish Labour leader Kezia Dugdale said: "This is a barbaric and sickening attack, targeted at young and vulnerable people enjoying a night at a concert".
He concluded saying: "This wicked ideology must be obliterated - and I mean completely obliterated - and the innocent life must be protected". Footage from the concert shows people fleeing on foot from the arena, where heavily armed police had swarmed.
After Manchester, Grande was to perform at venues in Europe, including Belgium, Poland, Germany, Switzerland and France, with concerts in Latin America and Asia to follow.
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