Staff at King’s Lynn’s Queen Elizabeth Hospital were urged to work if they could over the weekend as the hospital faced significant pressure.
A message was posted on social media calling for staff to help out.
Chief executive Jon Green said: “Due to large numbers of seriously unwell patients arriving at the hospital along with significant levels of staff sickness, we called an Internal Critical Incident.
“While the situation has been challenging and we have had beds available, I would like to praise all of our front line staff for the dedication and hard work to care for our acutely unwell patients.
“During this time we have also worked closely with partners across the healthcare system.”
Residents shared photos on social media of ambulances queuing at A and E.
A Facebook post by Elaine Auker, the relative of a patient, was shared more than 760 times. It said: “We were one of 13 ambulances waiting.
“The hospital was absolutely full to capacity, we finally got to the A and E corridor and that’s when I saw exactly what pressure those doctors, nurses and especially the paramedics were under.
“At one point there were 22 ambulances queued outside.
“I truly don’t know how the staff cope I have nothing but total admiration for them all especially the paramedics.”
Mr Green said: “Our priority remains patient safety and our staff have worked exceptionally hard to maintain this at all times.”
He reminded patients to consider alternative options such as pharmacists, calling 111 or using the NHS choices app.