A virus has attacked the computer system of one of Melbourne's largest hospital networks, causing chaos for staff and patients who may face delays as a result.

Staff at Melbourne Health - the network which runs the Royal Melbourne Hospital - are urgently trying to repair damage to its IT system after a virus infected Windows XP computers.

The health network's website is not working and says it is "currently under maintenance".

An email sent to staff today said the virus had hit Melbourne Health's pathology department, causing staff to manually process specimens such as blood, tissue and urine samples instead of computers aiding the registration, testing and entry of results.

While the Blood Bank is still operating for the hospital, the email said only urgent pathology specimens would be processed due to delays involved in "manual work-arounds" and that staff needed to send faxes to the pathology department if they required urgent results.