There are concerns for passengers on three flights between Thailand, Australia and New Zealand could be infected with the measles.
A measles warning has been issued after a passenger travelling through Sydney Airport on their way from Thailand to New Zealand was diagnosed with the disease.
The traveller was infectious while travelling on Jetstar flight JQ28 from Thailand to Sydney on on March 18.
The next day, they flew on Jetstar flight JQ517 from Sydney to Melbourne and Virgin Australia flight VA99 from Melbourne to New Zealand.
NSW Health has urged anyone who was on the same flights or in Sydney's international and domestic airports on March 19 to check for symptoms until April 6.
It can take up to 18 days for symptoms to develop after a person comes into contact with an infectious person.
People are susceptible to measles if they have never had the disease and haven't received two doses of the measles vaccine.
'If you're unsure whether you've had two doses, it's safe to have another,' NSW Health's Vicky Sheppeard said in a statement on Thursday.
Symptoms include fever, sore eyes and a cough, followed by a red, blotchy rash spreading from the head and neck to the rest of the body.
Outbreaks of measles in popular tourist destinations in Southeast Asia make the risk for measles being imported into Australia at the moment is high, the department said.
There has been 26 measles case in NSW since Christmas.