Hospitals operated by one of Melbourne’s largest public health services are dealing with a significant IT system outage, but many services are continuing with limited disruption. 

Eastern Health was working to fix the outage on Thursday after declaring a code yellow internal emergency.

The IT blackout was originally blamed on a critical core switch outage, with Eastern Health saying there was no evidence of a cyber attack.

The health service later said an identification process determined the specific cause of the issue and remedial action was underway. 

“Business continuity processes and the return of several systems have allowed many services to continue as planned with limited interruption,” Eastern Health said in a statement.

“Where this has occurred, patients are being notified of any disruption.”

Elective surgery was continuing for most planned cases, the health service confirmed. 

Eastern Health reverted its hospital systems to “downtime” procedures and enacted business continuity plans in the wake of the outage. 

The service would keep staff, patients and healthcare partners informed about the situation, it said.

Eastern Health operates Angliss Hospital, Box Hill Hospital, Maroondah Hospital, Wantirna Health and Yarra Ranges Health, among other services.

Premier Daniel Andrews described the outage as an internal hardware issue and said contingency plans involved going back to paper when needed.

“I’m very confident they’ll get the system back online, back up and running,” he told reporters.

“In the meantime, they’ll work as part of a health system – not as just health services – to manage those issues.”

By Cassandra Morgan and Callum Godde in Melbourne