At least 22 people, including some children, were killed and 59 wounded when a suicide bomber struck as thousands of fans streamed out of a concert by US singer Ariana Grande in the English city of Manchester on Monday.

Prime Minister Theresa May said the incident was being treated as a terrorist attack, making it the deadliest militant assault in Britain since four British Muslims killed 52 people in suicide bombings on London’s transport system in July 2005.

Speaking outside her offices in London, she said: “Although it is not the first time Manchester has suffered in this way, it is the worst attack the city has experienced, and the worst ever to hit the north of England.”

Britain’s third biggest city was hit in 1996 by a massive car bomb planted at a shopping centre by the Irish Liberation Army (IRA) which wounded more than 200 people.

May says police believe they know the attacker’s identity but are not disclosing it immediately.

Police said the attacker died after detonating explosives shortly after 10:33 pm (5:33am Hong Kong time) at Manchester Arena, which has the capacity to hold 21,000 people.

Some eyewitnesses said it happened after the concert ended in the foyer of the arena that links to the adjacent railway station, Mail Online reported. Children were among the dead, police said.

“We believe, at this stage, the attack last night was conducted by one man,” Manchester Chief Constable Ian Hopkins told reporters.

“The priority is to establish whether he was acting alone or as part of a network.

“The attacker... died at the arena. We believe the attacker was carrying an improvised explosive device which he detonated causing this atrocity.”

World leaders expressed shock and horror at the suicide bombing. China’s President Xi Jinping sent his condolences to Britain’s Queen Elizabeth, Chinese state media reported.

Hong Kong officials have not received reports from travellers seeking assistance, a spokesman from the Immigration Department said.

“We are still trying to find out whether any Hongkongers have been injured in the event,” he said.

The Hong Kong Travel Industry Council (TIC) said there were no Hong Kong travel tour groups attending the concert.