AMBULANCES were diverted from the Royal Victoria hospital's new £150 million A&E department on Sunday evening due to large numbers of patients seeking treatment.
The Belfast Trust confirmed that some 999 vehicles were diverted to the Mater hospital's casualty unit in the north of the city as the Royal came under pressure.
A spokeswoman said the measure was put in place "to effectively manage capacity across our Emergency Department service".
The divert ended at 6am yesterday.
The development came as more than 50 health and social care organisations lobbied the Executive yesterday over the current state of the health service.
The publication 'One Voice - Time for Change' by the Northern Ireland Confederation for Health And Social Care calls on politicians to urgently implement the recommendations of two major reports.
Transforming Your Care, which aimed to concentrate care in the community sector and away from hospital care, has been heavily criticised over its slow roll-out.
The independent Donaldson report by former English chief medical officer Sir Liam Donaldson also called for an overhaul of the entire hospital system and raised concerns about who was actually running the service.
The new report pointed to increased life expectancy and the number of people living longer with more complex conditions requiring care packages.
Colm McKenna, chair of the Confederation, said their research was a call to action.
"Sir Liam Donaldson was very adamant in his report that we can have a world-class health and social care system, but we can't do it if we keep doing it the way we're going,” he told the BBC.
“Because of an ageing population, demographic changes, the need is growing by five to six per cent per annum - we can't continue with that.
"We're already spending 50 per cent of the total Northern Ireland budget on health and social care, that's likely to grow."
