Manchester attack: 22 dead and 59 hurt in suicide bombing
Twenty-two people, including children, have been killed and 59 injured in a suicide attack at Manchester Arena.
The blast happened in the foyer at 22:35 BST on Monday at the end of a concert by US singer Ariana Grande.
Police said the lone male attacker, who died in the blast, detonated a homemade bomb.
Relatives are using social media to hunt for missing loved ones, and an emergency number, 0161 856 9400, has been set up.
The prime minister has chaired a meeting of the government's emergency Cobra committee and is expected to travel to Manchester later.
Chief Constable Ian Hopkins said it was "the most horrific incident" the city had ever faced.
He said the "fast-moving investigation" was now working to establish whether the attacker "was acting alone or as part of a network".
Sixty ambulances attended the incident and those wounded are now being treated at six hospitals around the city.
The UK threat level has been has been judged to be severe for nearly three years - which means an attack is considered highly likely.
But in recent months the tempo of counter terrorist activity has been increasing with - on average - an arrest every day.
After the attack in Westminster by Khalid Masood in March, police and security officials have been warning that further attacks were almost inevitable.
But they also believed that those were more likely to be low-tech involving knives or vehicles. The fact that the Manchester attack involved explosives will worry them.
It may not have been at the level of complexity seen in Paris in 2015, when multiple attackers sent from Syria used guns and suicide belts, but it will still have required planning.
World leaders have expressed solidarity with the UK, including US President Donald Trump, who called those responsible "evil losers".
Police have established a help centre at Manchester City's Etihad Stadium, access Gate 11, for anyone who needs assistance in tracing loved ones.
Twitter has been flooded with appeals from relatives and friends of missing concertgoers via the hashtag #MissingInManchester.
Facebook also activated a safety check feature so that people can let their family and friends know they are safe.
The blast happened close to the entrance to Victoria railway and tram station. The 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 dangerous item.
Greater Manchester Mayor Andy Burnham said the city would "pull together", adding: "That's what we are. That's what we do. They won't win."
http://www.bbc.co.uk/news/uk-england-manchester-40010124 Snipped various eyewitness accounts, full article is much longer.