A code black has been declared at Dunedin Hospital because it has reached full capacity.
The Southern DHB said that the hospital's emergency department is still open, but it is calling on those who are unwell to see their family doctor so that the ED can be reserved for emergencies.
Early this morning there were 18 patients in the Emergency Department waiting for a bed, but only three beds were available on the wards.
Southern DHB chief executive Chris Fleming said there had been heavy demand for hospital services in the past 24 hours.
"We are doing our best to deal with this demand, but patients may experience delays and some operations have been postponed," he said.
"We are asking the public to go to their GP early, use the after-hours service and keep the ED for emergencies only."
The hospital had been trialling an escalation plan which outlined the processes staff would be required to follow when the hospital was experiencing high demand, or where capacity exceeded available access to services.
Emergency operations centre incident controller Megan Boivin said: "The plan has been put in action and a decision was made early this morning to declare the hospital in code black - critical situation.
"This means that we have established a modified emergency operations centre.
"Our teams have been working extremely hard to improve the flow of patients through the hospital and the situation has improved.
"We realise that the pressure on staff has been unrelenting and we are urgently working to manage this high occupancy within Dunedin Hospital to allow patients to flow through the system in a timely manner including those who present to ED."
Fleming said the problem was not isolated to the emergency department.
"This is not just an ED issue but a whole-of-system issue," he said.
"A code black enables a consistent and coordinated response to manage this situation."
Fleming said without this response the system would continue to be under pressure which would affect how patients were handled when they arrived for treatment at the hospital.