A man in his 30s has become the fourth person in Victoria diagnosed with measles in less than a week.
A public alert was issued on Monday, with the health department confirming each patient contracted the disease while overseas.
The other patients include a nine-month-old boy, a man in his 20s and a woman in her 30s.
They have all received treatment and are recovering.
"There are a large number of ongoing international measles outbreaks in Asia, Europe and America," chief health officer Dr Brett Sutton said, urging travellers to get the free measles-mump-rubella (MMR) vaccine.
"People who are planning overseas travel should ensure they have received vaccinations appropriate to travel, including an MMR vaccine if they do not have a history of two previous MMR vaccinations."
Patients linked to the latest four cases may have been infectious while at public places including Melbourne Airport's terminal two, Eastland shopping centre and a hotel and restaurant on Phillip Island between July 20 and Saturday.
So far this year there have been 30 confirmed cases of measles in Victoria.
In almost all cases people were not fully immunised and travelled overseas or were in contact with overseas travellers.
Australian Associated Press