Up to 14 operations were cancelled at the Mid Western Regional Hospital in Limerick this morning after smoke triggered a fire alarm.
A motor overheated on the roof of the operating theatre block and smoke entered though a ventilation vent at around 11.30am, according to the HSE.
A HSE spokesman said the theatre block was evacuated along with an adjoining surgical day ward.
"When the alarm sounded, the hospital's technical services staff went to the plant room on the roof and made it safe.
"Limerick Fire Brigade was called to the hospital and the area was later inspected by the fire authorities. No damage and no injuries were caused in the incident."
HSE health and safety officials were due to carry out a further inspection at the scene this afternoon before the theatre block was returned to service.
The Mid Western Regional hospital apologised for the inconvenience caused to patients and their families and said new appointments will be scheduled as quickly as possible.
The Irish Patients Association called for an urgent investigation into how the incident occurred.
"We welcome the fact that no patients or staff were hurt," said spokesman Stephen McMahon.
"However questions have to be asked how this motor equipment was allowed to overheat and when it was last serviced.
"We would also call for an inspection of similar equipment in the Mid Western Hospital and in other hospitals."