Emergency doctors needed torches to treat patients during a power outage after the hospital's back-up system failed.
An investigation is underway after intermittent power loss at Hawke's Bay Hospital on Saturday. It's believed to have been caused by a faulty automatic switch.
Some parts of the hospital were without power for 30 minutes between 11.45am and 1.04pm as the hospital's three generators were inconsistent in delivering back-up electricity.
All lifesaving equipment such as ventilators in the Intensive Care Unit continued operating "successfully" through independent battery power, Hawke's Bay District Health Board chief executive Dr Kevin Snee said.
A hospital spokesman said operating theatres were not being used at the time but some patients on dialysis machines had to be taken off early.