Greater Manchester Police are working closely with the national counter-terrorism policing network and UK intelligence partners to investigate the concert explosion on Monday evening.
Ian Hopkins, Chief Constable of GMB, said: "We are doing all that we can, working with local and national agencies to support those affected as we gather information about what happened last night.
"This is clearly a very concerning time for everyone.
"I ask people to remain vigilant and if they have any concerns at all, to report them to the national anti-terrorist hotline on 0800 789321."
New CCTV of the Manchester bomber Salman Abedi has been released by police.
The younger brother of the Manchester bomber has said Salman Abedi was radicalised online in Britain.