The Waikato District Health Board (DHB) computer system, struck down by a virus, could continue to cripple the system for the weekend.
The Conficker virus was spotted at about 2am on Thursday, infecting 3000 computers logged on to the DHB's network and forcing a complete shut down.
The DHB had hoped to restart computers in key locations, including the emergency department and intensive care unit, on Friday morning but now says the original midday target is unrealistic.
"We're planning now to be out of action for the rest of the day, and in fact our emergency management team is planning that we may be down for the whole weekend," DHB spokeswoman Mary Anne Gill says.
"We've got connectivity between Bay of Plenty District Health Board and us, we run a joint diagnostic system, so that's up and running. We've also isolated an area that is virus-free, and we're doing all the testing there."
The shutdown has affected hospitals' radiology and lab testing services, and the DHB has asked all non-urgent patients to stay away.
Hamilton, Taumarunui, Te Kuiti, Tokoroa and Thames hospitals, as well other facilities in Te Awamutu and Morrinsville, have all been affected.
Gill says patient safety is paramount and the outage will not stop their care.
"We need to stop and say `look, computers don't diagnose and treat patients, doctors and nurses do that', and that's what our doctors and nurses are doing."
It was not yet known how the virus found its way into the system, but all computers were fully up to date with anti-virus software, she says.
Conficker is a so-called computer worm which targets Microsoft's Windows operating system, using flaws in the software to co-opt machines, allowing a remote user to take control.
A New York Times report has said the virus had affected millions of computers in more than 200 countries.
