Twenty-two people have been killed and 59 injured in an explosion at the end of a concert by US singer Ariana Grande at Manchester Arena.
Here is what we know so far.
The explosion happened in the foyer of Manchester Arena on Monday night, as people began leaving the concert.
Police were called at 22:33 BST.
Children are among the 22 killed in the explosion, police said. A further 59 people were injured.
Eyewitnesses described seeing metal nuts and bolts strewn around the floor and the smell of explosives. They also spoke about the fear and confusion that gripped concert-goers.
More than 240 emergency calls were made; 60 ambulances and 400 police officers attended.
Streets surrounding the arena and Victoria Station were sealed off.
After the attack hundreds of people in Manchester took to social media to offer spare beds and rooms for those stranded in the city.
Who carried out the attack?
Police say a lone male suicide bomber detonated an improvised explosive device, and died at the scene.
They are investigating whether he acted alone or was part of a wider network.
Greater Manchester Police chief constable Ian Hopkins said the force would treat the incident as a terror attack “until we have further information”
What has happened to those involved?
The injured are being treated at hospitals across Greater Manchester.
A hotline has been set up for people concerned about loved ones – on 0161 856 9400 and 0161 856 9900.
A help centre for anyone needing assistance has also been set up at Gate 11 of Manchester City’s Etihad Stadium.
Relatives are using social media to hunt for missing loved ones.
How have politicians responded?
Prime Minister Theresa May condemned the “appalling terrorist attack”.
“All our thoughts are with the victims and the families of those who have been affected,” she said.
She is chairing a meeting of the emergency committee Cobra on Tuesday morning.
All general election campaigning has been suspended until further notice.
A union jack has been lowered to half mast in Downing Street.
What disruption has been caused?
A cordon remains in place around Manchester Arena and Victoria Station while forensic work is carried out.
All train services to and from Victoria station have been cancelled.
What do we know about the investigation?
If the bombing is confirmed to be a terrorist attack, it would be the worst in the UK since 52 people were killed in the London bombings of July 2005.
Anyone with information can call the anti-terror hotline on 0800 789321.
The police have also appealed to anyone with images or footage from last night that they believe could assist in the investigations to upload it to ukpoliceimageappeal.co.uk or ukpoliceimageappeal.com