Ambulances queued outside all NI hospital emergency departments on Tuesday as they struggled with covid pressures, the ambulance service said.
Doctors treated patients in ambulances outside Antrim Area Hospital due to the hospital operating beyond capacity.
At 17:00 GMT on Tuesday, 17 ambulances were queued outside, although this had dropped to four by 20:45.
By 22:30 the ambulance service said it was not experiencing any major problems.
Amid the pressure, politicians were urged to urgently rethink loosening covid rules over Christmas.
Northern Health Trust operations director Wendy Magowan said it was the first time she had witnessed such a situation at Antrim Hospital.
Speaking on Tuesday evening, Dr Nigel Ruddle, medical director of the Northern Ireland Ambulance Service, said: "All of the emergency departments in Northern Ireland are seeing ambulances queued outside to various degrees.
"We are seeing the pressures right across Northern Ireland."
Health minister Robin Swann confirmed he would bring new proposals about restrictions to Thursday's executive meeting.
The meeting will see ministers look at options to manage the spread of Covid-19 in Northern Ireland.
A further six Covid-19 related deaths were reported in Northern Ireland by the Department of Health, taking its total to 1,135.
There have been 59,121 positive tests after another 486 were recorded.
There are 87 outbreaks of the virus in NI care homes, while hospital occupancy levels are at 104%.
The reproduction rate of the virus in Northern Ireland remains at or slightly above 1, according to health chiefs.
'Numbers are rising'
Northern Trust executive Ms Magowan said: "This has never happened in Antrim hospital before in my memory, never.
"We got to a situation last night that we had so many people waiting in ED to get into beds that we simply had no room left.
"We haven't got out of the second surge, in fact, our numbers are rising. We have the highest number of inpatients today that we've ever had with Covid.
"If this doubles, I don't know how we're going to make it through."
Pat Cullen from the Royal College of Nursing told the BBC's Evening Extra programme that nurses were exhausted from working "excessive hours".
She said hospital nurses were treating patients in the back of ambulances and along corridors as well as on the wards and in the emergency departments, while the district nurses were trying to cope with "60% vacancies" in their workforce.
She said: "Speaking to many of our nurses today, there's no doubt that this is the closest I've ever seen nurses to being totally burnt out.
"Exhausted isn't even a word to describe how the nurses feel.
"At this moment in time, a 12-hour shift almost seems a luxury to them - they're working well beyond that."
At a briefing on Tuesday, Chief Medical Officer Dr Michael McBride and Chief Scientific Adviser Prof Ian Young told journalists that numbers were not where they would like them to be.
They also gave a stark warning that any third wave would come on top of already "stubbornly high" hospital in-patient numbers.
Prof Young said: "The position is very different to what it was first wave and second wave of this virus.
"At the beginning of the first wave we had no hospital in patients with Covid.
"At the beginning of the second wave the numbers about 20.
"If we see an increase in numbers again as a consequence of the current position, then it will be an increase of numbers on top of a baseline of 300-400 people in hospital. And the numbers will only rise from there."
I was at Antrim Area Hospital this morning until about midday and what I witnessed was a system that is clearly just hanging together.
I saw staff clearly exhausted and anxious and they were the staff who were outside in the ambulance bay.
The problem is that the ambulances had nowhere to go, they couldn't unload their patients inside, so I also watched as doctors stepped inside ambulances, wearing their PPE, triaging those patients inside the ambulances, making decisions about who should be taken in first.
The picture was a really sorry one, a stark one and this is really at the start of what could become an incredibly busy period.
Prof Young urged people to stick with the guidelines over the festive period and said anyone who was forming a Christmas bubble should not see anyone else for the next 10 days.
Dr McBride revealed he would not be hosting family or friends this Christmas - having discussed the issue with elderly parents and children.
He said now was the "best time for the virus" but worst time for the health service.
Health minister Robin Swann told the assembly the two-week limited lockdown which ended on 10 December had seen a "stabilisation" of the virus but the figures were still too high.
He said he would not pre-empt Thursday's executive meeting and provide details of suggestions he would put forward.
Deputy First Minister Michelle O'Neill said Sinn Féin "will support any proposals brought forward by the health minister to tackle the current situation."
She added: "It is clear we are facing a very dangerous situation with the spread of Covid-19, the rise in hospitalisations and, sadly, people losing their lives."
“It is clear we are facing a very dangerous situation with the spread of COVID-19, the rise in hospitalisations and, sadly, people losing their lives.— Michelle O’Neill (@moneillsf) December 15, 2020
“Sinn Féin will support any proposals brought forward by the health minister to tackle the current situation.” https://t.co/FLSXzUFRse
Further talks over whether to revise Covid rules over Christmas will take place between the UK government and the devolved governments on Wednesday.
Cabinet minister Michael Gove discussed the issue with senior politicians in Scotland, Northern Ireland and Wales on Tuesday, but no final decision was made.
It also emerged on Tuesday that vaccinators have been in all five health trusts.
Mr Swann told the assembly the Covid-19 vaccine had now been delivered in up to 54 care homes, starting with those with the largest numbers of residents.
About 4,000 people in NI have been vaccinated so far.
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A second delivery of the vaccine arrived in Northern Ireland at the weekend, meaning around 50,000 doses are now available.
The vaccine requires two doses to be given, three weeks apart, to be effective.