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 9400.
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.
The explosion happened in the arena's foyer shortly after the concert ended, close to the entrance to Victoria train and tram station.
The station has been closed and all trains cancelled.