Target times for the most urgent 999 calls have been repeatedly missed over the past week, UTV can reveal.
Ambulance chiefs have said it is the worst position they have ever been in.
At one point over the new year period, between December 30 and January 5, the pressures on the service got to such an extent that a category one call - the most serious - left someone waiting for 45 minutes.
The target time is eight minutes.
The pressure is coming mainly from staff absences due to the pandemic, rather than patient numbers.
Ambulance Service chiefs have brought in extra resources to cope.
Dr Nigel Ruddell from the Northern Ireland Ambulance Service told UTV anyone facing a delay for an ambulance was at risk of further harm, or of dying.
"I don't at present have any evidence of anyone who has died as a result of delays but nonetheless anybody who is waiting too long for an ambulance to arrive is suffering harm in some shape or form," he said.
The most life-threatening calls are only a small proportion of what first responders have to deal with.
Alan Emerson who is terminally ill became seriously ill in the past week but no ambulance was available for hours.
In the end his family were told to drive him to an A&E. He is now recovering from sepsis at home.
His son Robin said he was not surprised by these latest figures.
"I know with my daughter Georgia where we have had weekly 999 calls before with her seizures, where she stops breathing, every second counts. One minute is the difference between life and death," he said.
He said patients deserved a system that worked and that was fit for purpose.
"A friend of mine who is a pilot doesn't say, 'I'll try my best and land you close to the airport'."
Dr Ruddell said a lot of work was going into prioritising and diverting resources to the frontline.
"We've been bringing in representatives from the voluntary and the independent ambulance services to help bolster our numbers during this difficult time," he said.
"But we do appreciate that there are people who will have to wait longer and we apologise for that."