There has been a "dramatic deterioration" in ambulance handover times in Northern Ireland, according to a new report.
The number of handovers taking more than three hours rose from around 400 (less than 1%) in 2019/20 to just over 11,000 (9%) in 2023/24.
The report by Northern Ireland's Comptroller and Auditor General Dorinnia Carville found that these delays led to tens of thousands of instances of potential harm to patients.
It comes as hospital emergency departments (EDs) across the region continue to be under pressure with high volumes of patients.
Earlier this year, Dr Nigel Ruddell, the medical director of the Northern Ireland Ambulance Service (NIAS), said that delays getting patients into emergency departments was leading to an increase in deaths.
The Auditor General's report, which pertains to the year 2023/24, found more than 36,000 instances in 2023/24 when patients may have potentially experienced some harm as a result of ambulance handover delays.
It also found around 3,800 occasions when patients were potentially subject to severe harm.
Ms Carville said "in 2020 we saw four deaths as a result of ambulance handover delays, last year that had risen to 31 deaths".
The report considers performance relating to the process of moving a patient from an ambulance into an emergency department to be seen by medical and nursing staff, and highlighted a "worsening performance" against the NIAS target of completing handovers within 15 minutes.
It found that in 2019/20, around 27% of handovers were completed in this time frame compared with 7% in 2023/24.
It also described the overall performance throughout Northern Ireland as much worse than in England and Wales.
The report outlined the impact of the longer times for ambulance handovers as including an estimated £50 million of lost operational capacity in NIAS between 2019/20 and 2023/24, with 25% of operational capacity lost in 2023/24 due to delays.
It also found a deterioration in NIAS performance when responding to 999 calls because of ambulances being increasingly tied up waiting outside emergency departments, and noted particular concerns around performance in relation to emergencies and potentially serious incidents.
Meanwhile, the report found an increased reliance on the unregulated private sector to address service provision gaps. In 2019/20, NIAS commissioned private sector ambulances to provide emergency department relief on more than 20 occasions. By 2023/24, this had risen to more than 1,000 occasions.
It noted that the delays in ambulance handovers were interconnected with other, well-publicised challenges and pressures on the health service, such as limited bed space within hospitals and delays in discharging patients fit to leave hospitals.
The report also referenced other department-commissioned research which cited ambulance handover delays as the single biggest risk to patients in the emergency care system in the region.
Ms Carville described the length of time ambulances were waiting outside hospitals as "unacceptable".
She said: "We have also seen the number of deaths increase in the period, in 2020 we saw four deaths as a result of ambulance handover delays, last year that had risen to 31 deaths."
"Having ambulances waiting outside hospitals for lengthy periods of time is both unacceptable for patient well-being and a waste of public resources," she said.
"Addressing this issue will no doubt be challenging. However, this report includes recommendations, and good practice from other regions, highlighting key areas for improvement.
"In particular, we have stressed the need for strong leadership to help break down siloed working and instil a culture that sees patients as the responsibility of hospitals and trusts when an ambulance arrives at a hospital, and not just once the handover process is complete."
