The Canterbury District Health Board has confirmed that the pre-booked surgeries had to be rescheduled last week.
Acting executive director, planning, funding and decision support Ralph La Salle said the hospital was swamped with surgeries that did not require an overnight stay.
He said it was the only way to free up beds for a surge of patients coming in, who were acutely unwell.
Patients arrived with a range of health conditions in the emergency department, by ambulance, or from their doctors.
He said they needed to free up beds for a surge in the number of "acutely unwell" people who needed hospital-level care as an inpatient.
"We realise this is disruptive and frustrating for those whose pre-booked surgery had to be delayed and rescheduled, and we apologise for that.
"However, it's the only way we can free up beds for people coming in acutely unwell and requiring a hospital admission," La Salle said.
People were admitted for a wide range of health conditions and all CDHB hospitals were busy last week, he said.
"Many of the people who needed to be admitted came in via the emergency department, while others were referred by their GP, or came via ambulance."
