Twenty-two people have been killed and 59 injured in a suicide bombing at Manchester Arena, at the end of a concert by US singer Ariana Grande.
Eight-year-old Saffie Roussos and Georgina Callander, believed to be 18, are among the dead.
Security services believe they know the attacker’s identity but are not yet able to confirm it.
The streets of Manchester are deserted in the wake of the attack at the arena.
Relatives are using social media to hunt for loved ones, and an emergency number, 0800 096 0095, has been set up.
People have been laying tributes around the city.
Prime Minister Theresa May has condemned the Manchester Arena attack saying it was an “appalling, sickening” terrorist act.
Flags are flying at half mast outside Number 10 and above the Houses of Parliament. Political parties have suspended general election campaigning.
Police forensic officers are continuing to investigate the scene of the explosion.
The Arndale shopping centre in Manchester was briefly evacuated on Tuesday, but is now reopening.