Only one ambulance crew was in operation in the entire Craigavon area on Saturday night, the Portadown Times has learned.
According to the NI Ambulance Service, staff shortages meant only one crew instead of the normal two crews manned the region which extends from Dungannon to Moira, Lurgan, Portadown and Armagh.
The NIAS said one third of ambulances normally on duty across the province were unavailable due to too few staff and this led to delays in its 999 response times at the weekend.
The internal review has been ordered.
One member of the ambulance service said morale among staff locally was ‘at rock bottom’.
He said staff are working without food breaks and longer than their allotted hours leaving them “wrecked”. He explained that because there is a staff shortage, employees are being denied leave and many are calling in sick.
The NIAS director of operations, Brian McNeill, said, “We dropped our cover levels down to 71 per cent, which put a lot of pressure on the people who actually came to work that night.”
He said all 999 calls were answered and there had been no reports of “serious adverse incidents” but he added that ambulance response times were “slower than we would have liked”.
Mr McNeill said a number of factors, including unfilled posts and late notification of sickness absence, had contributed to the weekend staff shortage.
He said that 13 per cent of jobs within the NIAS are currently vacant.
The Northern Ireland Ambulance Branch of the Unison trade union said the drop in accident and emergency ambulance cover at weekends was “a symptom of a larger financial issue” and it blamed efficiency savings “imposed by the Department of Health”.
“Simply put, the operational staff are required to answer more 999 calls with fewer ambulances available to do so,” the union said in a statement.
“This has had the knock-on effect of 999 crews having to work through their meal breaks and being hours late off duty at the end of their shift.”
The union said there are “approximately 100 vacancies at Emergency Medical Technician grade” within the NIAS and ambulance crews were “often left standing for hours in hospital corridors waiting to off-load their patients”.
A Craigavon Hospital spokesperson said, “Craigavon Area Hospital was operating as normal at the weekend and there were no issues to report.”