Police, fire service and ambulance personnel have been spotted outside Manchester arena today (February 28).
The emergency workers are taking part in a large-scare training exercise to test their ability to work together.
It comes almost five years after communications failures between agencies blighted their response to the terror attack at the venue which claimed 22 lives and injured a thousand others.
Greater Manchester Police said the training involved a 'mock scenario' - they declined to reveal what the scenario is, but said it is not counter terrorism.
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The training is taking place at and around the AO Arena, formerly Manchester Arena.
The force said in a statement: "Greater Manchester Police and partner agencies will today (Monday 28 February 2022) take part in an exercise in Manchester City Centre.
"The exercise is not a real incident or emergency. It is a mock scenario, not related to counter terrorism policing.
"This is a test of the multi-agency response to incidents and emergencies, ensuring we work together to deliver an outstanding service."
Pictures from the scene showed the police, fire and ambulance services at the scene.
In an updated statement, GMP said: "Based on a mock scenario, not related to counter terrorism policing, the exercise tested the multi-agency response to incidents and emergencies, ensuring we work together to deliver an outstanding service."
Inspector Edward Goss, of GMP's Specialist Operation Branch, added: "It is really important for police officers and staff, alongside partner agencies, to be given opportunities to test the response to incidents and emergencies like this.
"Exercises support our value to be a learning organisation which delivers outstanding service whilst keeping people safe and caring for victims.
"I would like to use this opportunity to thank members of the public who were in the area at the time for their cooperation. I would also like to thank our partner agencies, particularly the AO Arena, for their involvement in this exercise."
Greater Manchester Police has admitted a series of deficiencies , centred around a failure to communicate with other emergency services and training in connection with the May 2017 Manchester Arena bombing, and has formally apologised twice at the continuing public inquiry into the disaster.
Greater Manchester Fire and Rescue Service has also apologised but blamed 'silence' from the police.
It was more than two hours before the first firefighters arrived at the scene.
The M.E.N. reported yesterday that families of the some of the 22 who died in that 2017 suicide bombing believe that even today - almost five years later - the force is trying to 'completely offload responsibility' to one officer, and to suggest its admitted failures that night actually made no difference at all to the toll of dead and injured.
The force duty officer on the night of the attack, Dale Sexton, didn't share vital information with the other emergency services, the inquiry has been told.