Dunedin Hospital is in "code black" with the number of people needing treatment exceeding the beds available.
About 18 of 32 people expecting to be admitted today were last night contacted by staff and told their procedures or surgery had been postponed because of the high number of unwell people who were unable to be discharged.
The hospital reaches "code black" status when it has fewer than six beds available.
Yesterday morning it had no free beds and, by mid-afternoon, 33 people waiting for treatment in the emergency department, Otago District Health Board operations manager Megan Boivin said.
There was one available bed at 8pm and 26 people waiting in the emergency department.
If no beds became available last night, those patients would stay overnight in the emergency department or an extra bed would be added in each ward.
There seemed to be no single reason for the high demand.
People were presenting with a range of problems from traumas to infections and flu, she said.
Usually, there would be a drop-off in admissions during a weekend.
This had not happened and the emergency department had also been consistently busy.
"We've just not discharged as many as we would, because of how unwell they are."
The hospital was above its occupancy rate for most of yesterday, with only 12 people discharged throughout the day.
The hospital had been on "code red", the next level down when fewer than 27 beds are free, since Friday.
Service management teams and medical staff were notified of the impending bed problem on Saturday afternoon, to ensure anyone who was well enough was discharged as soon as possible.
"That has not been a success, as people are unwell and unable to be discharged," Mrs Boivin said.
Staff were also looking to see if any patients could be transferred to home-town hospitals, she said.
Adding to the situation was increased staff sickness, which meant wards were not fully staffed.
Staff were being asked to do overtime or extra shifts to get through the busy period, she said.
The code black meant today's admissions were postponed to provide a buffer for the rest of the week, she said.
Thirty-two people were today scheduled to be admitted for elective procedures or surgery, and 25 to 30 acute admissions were expected.
It was hoped with more medical staff and community support available at the start of the working week, about 25 people could be discharged today.
"We'll be assessing it hour by hour."
Despite the overcrowding, Mrs Boivin urged people to continue to go to hospital if necessary, but if they did not think it was an emergency, to see their family doctor or after-hours service first.
Dunedin Hospital previously reached code black for two days in February.
