There have now been 13 confirmed measles cases in the Perth metropolitan area since mid-September.

While the majority of people infected with measles predominantly live in the Rockingham area, experts warned the risk of exposure applied to travellers travelling on flight NZ175, which arrived in Perth on September 23. Other people within the broader metropolitan area may also unknowingly been exposed.

Perth has recorded 13 cases of measles since mid-September. Credit:Shutterstock

The Health Department on Friday warned children and adults not immune were at risk of developing measles if they were inadvertently exposed and should remain vigilant for the onset of symptoms for the next three weeks.

Communicable Disease Control Directorate acting director Dr Paul Effler said measles was a serious and highly contagious viral illness spread by tiny droplets released when infected people cough and sneeze.