Twenty-two people, including children, are now known to have been killed and 59 injured in a suspected terror attack at Manchester Arena.
The blast happened at 22:35 BST on Monday at the end of a pop concert by the US singer Ariana Grande.
Greater Manchester Police said the lone male attacker, who died in the blast, was carrying an improvised explosive device which he detonated.
Relatives are using social media to hunt for missing loved ones.
Police have set up an emergency telephone number in response to the attack. It is: 0161 856 940
Home Secretary Amber Rudd said it was “a barbaric attack, deliberately targeting some of the most vulnerable”.
The prime minister is to chair a meeting of the government’s emergency Cobra committee at around 09:00 BST.
In light of the attack, political parties have suspended campaigning ahead of the general election.
The explosion occurred shortly after Ariana Grande left the stage at the arena – the city’s largest indoor venue with a concert capacity of around 21,000.
Grande – a 23-year-old American TV teen actress-turned-pop star – has a strong following among teenage girls and children.
The pop star tweeted: “broken. from the bottom of my heart, i am so so sorry. i don’t have words.”
The blast occurred close to the entrance to Victoria train and tram station has been closed and all trains cancelled.
Police also carried out a precautionary controlled explosion in the Cathedral Garden area of the city at about 01:32. The force later confirmed it was not a suspicious item.