Police said they were called at 10:33 pm (2133 GMT) Monday to reports of an explosion at Manchester Arena.
Here is what we know so far about Monday's attack, the deadliest in Britain since 2005.
Police said they were called at 10:33 pm (2133 GMT) Monday to reports of an explosion at Manchester Arena during a concert by US pop star Ariana Grande, who is popular with teenagers and pre-teens.
Witnesses described a "huge bomb-like bang" and scenes of panic as young fans rushed out and parents waiting outside searched frantically for their children.
Prime Minister Theresa May condemned the attack for its "appalling sickening cowardice" and for "deliberately targeting innocent defenceless children and young people".
The bomber used an improvised explosive device apparently packed with nails and other metal objects, outside one of the exits at the 21,000-capacity arena.
The suspected bomber has been identified as 22-year-old Salman Abedi, a British student dropout born to Libyan parents who fled the regime of slain dictator Moamer Kadhafi.
Interior minister Amber Rudd confirmed on Wednesday he was known to intelligence services and that it was "likely" he was not working alone.
Her French counterpart Gerard Collomb said Abedi had become radicalised after a trip to Libya and probably Syria, according to information received from British intelligence services.
"In any case, the links with Daesh are proven," he said, using another term for the so-called Islamic State group.
IS on Tuesday claimed responsibility through its social media channels, saying "one of the caliphate's soldiers placed bombs among the crowds", and threatening more attacks.
British police on Wednesday made three more arrests over the attack, after detaining a 23-year-old man on Tuesday. Police also carried out raids in the south Manchester area of Fallowfield where Abedi lived.
May said the 22 dead and 59 injured included "many children and young people". Many of those taken to hospital are suffering life-threatening conditions
Eight-year-old Saffie Rose Roussos is so far the youngest named victim. She attended the concert with her mother and older sister, who were both injured.
Olivia Campbell, 15, was confirmed dead on Wednesday by her mother, who had issued heartrending appeals for help when her daughter was still listed as missing.
A Polish couple living in Britain, identified as Angelika and Marcin Klis, were also caught in the explosion as they went to collect their daughters.
May on Tuesday placed the country on its highest level of terror alert -- "critical" -- meaning a new attack is believed to be imminent.
Soldiers are being sent to assist armed police to protect strategic sites. The last time troops were deployed on British streets was in 2007.
The troop plan, codenamed Operation Temperer, was first revealed after the November 2015 Paris attacks and is believed to allow up to 5,000 soldiers to be deployed.
Major sports venues plan to beef up security, with several high profile events in the coming weeks, including the FA Cup final at Wembley on Saturday.
The Changing of the Guard outside Buckingham Palace was cancelled on Wednesday and parliament suspended all public events.
Manchester United's Europa League final against Ajax in Stockholm on Wednesday is still set to go ahead under tight security.
Downing Street said May will still attend the NATO summit in Brussels on Thursday and the meeting of G7 leaders in Sicily on Friday and Saturday.
The Manchester bombing is Britain's second terror attack in two months.
On March 22, five people were killed and more than 50 injured when a man ploughed into pedestrians on Westminster Bridge in central London, before crashing into the fence surrounding parliament.
The attacker, 52-year-old Khalid Masood, fatally stabbed a police officer before being shot dead by police outside parliament.
Investigators described that attack as "Islamist-related terrorism" but have not charged anyone over the incident.
The deadliest bomb attack on British soil took place on July 7, 2005 when four British suicide bombers inspired by Al-Qaeda attacked London's transport system, killing 52 people and wounding 700.