An inquiry into the Manchester Arena bombing has heard there were only seven ambulances on the scene to treat people when the bomb went off.
There were 76 ambulances already responding to other emergencies across Greater Manchester on the evening of the 22nd of May 2017.
Today a senior clinician told the inquiry those "logistical problems" explained why some casualties who required immediate critical care treatment waited for up to three hours at the arena before they were taken to hospital.
Mr Tunn claimed he was "astonished", and it was a "tribute to the rest of the NHS", that by 11.15pm - nearly 45 minutes after the blast - there were around 25 ambulances available as a total of 59 people were eventually taken to hospital.
Inquiry chairman Sir John Saunders asked: "So it took a while to get the necessary ambulances there who were available to take people to hospital, that's the delay really, is it?"
Dr Tunn replied: "I think that's a very fair reflection, it's the reality."
Lisa Roberts QC, who is representing NWAS, said that calls kept coming through to the ambulance service into the early hours requiring attendance in Manchester and other parts of the North West.
He told her: "The public often respond really helpfully and reduce their demand on ambulances, but it doesn't disappear because people can't stop having heart attacks and so on, or having babies."
Dr Tunn went to the scene with his paramedic son to help with the emergency response after his boss called him at home to give him a "heads up" that a "serious and sizeable" incident had taken place.
The inquiry into the attack in which suicide bomber Salman Abedi detonated his device at the end of an Ariana Grande concert, killing 22 people and injuring hundreds others, continues next Monday.