Christchurch Hospital was plunged into darkness for an hour on Friday night after an unexplained power outage.
Generators at the hospital failed to switch on - the first time an electric disruption of this scale has hit the hospital.
"The power went off at about 24 mins past 8pm and usually the generators kick in but they didn't, so the power was off for nearly an hour," said emergency management clinical nurse manager Tracey Williams.
The outage affected all hospital systems.
"We not only lost power to the monitors, we lost power to computers, cell phones so we couldn't communicate with anyone outside of the department," she said.
There were 478 patients in the building at the time, including 96 in the emergency department.
One nurse who did not want to be named said when the power went down they just had to adapt - but she praised the communication from hospital teams.
Newshub also spoke to a man who got locked out of the ward his mother was in, and described nurses using torches to find their way through the building.
"Everybody was safe, there was no risk to patients or staff, it was just really inconvenient," Williams said.
"It was definitely a new experience doing suturing by torchlight," said registered nurse children's emergency Shannon Burrows.
Hospital staff are now investigating why the generators did not automatically kick in.
On Saturday, power company Connetics were spotted repairing one of two cables that feed into the hospital network supply.
"We have a storage of torches although we will probably need to review how many we’ve got," said Williams.
While Friday night's outage was brief and under control, questions remain about what happened at a hospital that's home to one of the busiest emergency departments in the country.
