Acting chief executive officer Andrew Trigg said the impact could result in a number of cancellations for dental patients.

"Should this occur, the affected patients will be individually contacted by phone," he said.

All other SWH patient service remain unaffected.

Anyone who wants additional reassurance that their surgical, medical, dental, GP clinic community health and/or mental health appointments are unaffected can contact the 24/7 SWH hotline on 5564 4253.

Yesterday: Internal communication issues at Warrnambool Base Hospital caused by a cyber attack are being managed using a range of initiatives, including fax machines.

South West Healthcare acting chief executive officer Andrew Trigg said staff were more heavily relying on phones and faxes.

He said specific incident control groups had been established.

"Staff are being regularly updated via Facebook, notice boards, a daily (hard copy) communique and regular face-to-face management updates," he said.

"Many paperless-related activities have been swapped for hard copy.

"We want to assure everyone that none of the above is impacting on the services to our patients, inpatients, consumers, users and residents.

"And we are confident patient confidentiality has not been compromised."

Mr Trigg said business systems had been impacted and alternative arrangements were being implemented.

"We remain confident wages and invoices will be paid as normal," he said.

Anyone wanting additional reassurance that their surgical medical, dental, community health and/or mental health appointments are unaffected can contact the SWH hotline on 5564 4253.

It's understood that patient services are unaffected and there are no cyber security-related surgery cancellations.

At 11.15am: Portland District Health is asking the community to be patient and to reconfirm appointments by phone as it deals with the fallout of a cyber attack.

PDH has also assured local people their information is protected and that the health service is continuing to offer safe services.

Chief executive officer Chris Giles said there was no indication at this time that personal patient information had been accessed by the hackers.

"Patient care has not been compromised by the attack on our network," she said.

PDH was one of several hospitals in south-west Victoria and Gippsland to have their information technology systems impacted by a cyber attack, including Warrnambool, Hamilton, Portland, Port Fairy and Colac hospitals.

PDH is part of the South West Alliance of Rural Health (SWARH) network which was his by the attack.

The Gippsland Health Alliance has also been attacked.

South West Healthcare, Colac Area Health, Latrobe Regional Hospital and University Hospital Geelong are among the health services affected.

"All our data is safe, but with the internet down, it is causing disruptions to accessing systems," Ms Giles said.

"Our focus is to continue to provide safe high-quality services to our community and we have manual back-up processes in place to ensure this occurs."

Ms Giles said the biggest patient impact was in specialist consulting suite clinics as the booking and appointment system was not available.

"We are asking patients to call us before they attend the specialist clinic to confirm their appointment," Ms Giles said.

The Portland health numbers to call are 5522 1410 or 5522 1417.

"We are manually working on our booking system to minimise impact and rescheduling some appointments if needed," she said.

No surgeries have been cancelled and emergency services are continuing as normal.

"If there are any emergencies people can still attend as usual for medical assistance," Ms Giles said.

The cyber attack was uncovered on Monday and PDH and other health services have been warned their information systems may be impacted for up to two weeks.

Ms Giles said a number of systems at PDH had been isolated and disconnected to quarantine the infection, including the internet and email system.

The state government is working with the impacted health services, Victoria Police and the Australian Cyber Security Centre to manage the incident, in which the infiltration of ransomware blocked access to several systems.

Safer Care Victoria is working with the health services to help assess and manage patients.

A Victoria Police spokeswoman said detectives from the E Crime Squad were investigating a cyber-security incident involving a number of hospitals in western Victoria.

"The data breach was reported to police by the Department of Health and Human Services yesterday," she said.

"The hospitals have taken a number of steps to quarantine the infection and further work is being undertaken to remedy the situation. The investigation by Victoria Police remains ongoing," she said.

Earlier: As a top Australian spy agency continues to investigate a cyber attack on the south-west hospital network, almost 30 patients have had surgeries cancelled across the state.

Barwon Health chief executive Frances Diver said 27 elective surgery cases had been cancelled over the past two days, while 140 procedures went ahead as planned.

"Yesterday we undertook about 50 elective surgery cases and we cancelled about 16," she said.

About 11 cases were cancelled on Wednesday.

"We are actually able to provide most of our services.

"It's just about individual clinicians going through each of the cases and determining if they can proceed with the surgery with the information available to them in theatre."

Hospitals linked to the South West Alliance of Rural Health - including Warrnambool, Portland, Hamilton, Port Fairy and Colac hospitals - and Gippsland Health Alliance and were among those targeted by ransomware on Monday.

Despite being unable to access internet or emails, a South West Healthcare spokeswoman maintains it's been business as usual at the hospital.

She said there have been no impacts from the cyber security attack.

"There are no cyber security related cancellations for any surgery and/or any other type of medical, dental, GP clinic, community health and mental health appointments," she said.

"We have set up a 24/7 hotline phone number for local people wanting assurances that Monday's cyber security incident has not affected upcoming appointments for any of our SWH patient services. That number is 5564 4253."

She said staff pay would not be impacted.

"We want our workforce and suppliers to know that while out business systems have been impacted, we are confident wages and invoices will be paid as normal.

"We still cannot send or receive emails."

Authorities denied personal patient information was accessed.

The centres isolated and disconnected a number of systems to quarantine the infection, as federal and Victorian authorities investigate.

The Australian Cyber Security Centre - part of the secretive Signals Directorate - alongside Victorian and federal police are probing the attack, and on Wednesday issued a general statement about hacking.

"Malicious cyber activity against Australia's national and economic interests is increasing in frequency, scale, sophistication and impact," the statement said.

"No internet-connected network is 100 per cent secure, and no single sector is immune."

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However, an auditor-general report released in May warned Victorian hospitals - including those under Barwon Health - that cybersecurity needed improvement.It is not clear how many of the report's 14 recommendations Barwon Health has implemented.

David Cullen, principal advisor to the Victorian government on cyber incidents, could not say how long it would take to get the systems running again or why the two hospital networks had been targeted.

But he admitted it would be "a long, complex and protracted forensic investigation".

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