Two people infected with measles in Bali

Two people have been diagnosed with measles after returning to Perth from Bali, prompting health authorities to issue a warning.

The two were members of a family who flew back to Perth on board Air Asia flight QZ548 from Denpasar at midday on Saturday.

The WA Health Department said passengers on the flight could have been exposed to the sick people while they were infectious and could be at risk of measles.

People could also have been exposed on Saturday at Perth Airport's international terminal, a Dan Murphy's bottleshop in Bull Creek, Pharmacy 777 in Willetton and an IGA supermarket in Willetton.

The community could also have been exposed on Sunday at Olympic Medical Centre in Canning Vale and the emergency department at Princess Margaret Hospital.

Communicable Disease Control medical co-ordinator Paul Effler said staff had been directly contacting individuals, but it was impossible to contact everyone who was in a public place.

"Measles is contagious for up to five days before the development of the rash and for four days after the rash starts," he said.

A person is considered immune to measles if they have received two doses of a measles vaccine or were born before 1966.

Anyone who may have measles should warn doctors before arriving for a consultation, to prevent infecting others, Dr Effler said.