A suicide bomber killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester.
Some 59 people were also injured in the blast when the attacker detonated an improvised explosive device at the Manchester Arena.
Announcing that the death toll had risen overnight, Greater Manchester Police chief constable Ian Hopkins said: “What I can confirm is that there are children among the deceased.”
He said: “This has been the most horrific incident we have had to face in Greater Manchester and one that we all hoped we would never see.
“Families and many young people were out to enjoy a concert at the Manchester Arena and have lost their lives.”
Mr Hopkins said investigators believed the attack was conducted by one man who died at the scene, although detectives are working to establish if he “was acting alone or as part of a network”.
Police were called to reports of an explosion at the Manchester Arena at 10.33pm, shortly after US singer Ariana Grande had finished her performance.
Victims described being thrown by the blast that scattered nuts and bolts across the floor.
More than 240 calls were made to the emergency services, with responders including 60 ambulances flooding the area.
More than 400 police officers were deployed as part of the operation, with a visible presence remaining on the streets of Manchester on Tuesday.
The injured are being treated at hospitals across Greater Manchester, and a hotline has been set up for those with concerns over loved ones who remain unaccounted for.
Police have appealed for concert-goers and witnesses to provide them with any footage they have from the scene if they believe it can assist the probe.