People across three states are being warned to be on high alert for measles symptoms after three people visited several locations over multiple days while infectious.

Plane and bus passengers have potentially been exposed to measles after a returned international traveller flew into Sydney's International Airport and travelled to the ACT by bus.

The infectious person flew into Sydney Airport from Dehli on Air India flight AI 302 on Saturday at 8.10pm before transiting through the terminal 1 international arrivals hall where they stopped at baggage claim and customs.

The person went to bay 9 in the bus and coach bays where they hopped on a Murrays Bus bound for Canberra.

ACT Health is contacting the bus passengers.

People who attended a Melbourne car dealership and an indoor sports centre may have been in contact with measles after another infectious overseas returned traveller visited the locations over several days.

Victoria's first reported measles case of 2024 was detected in the person who attended two sites in Melbourne's east and southeast between last Wednesday and Friday while infectious, Chief Health Officer Clare Looker said.

The person visited the Bay City Auto Group and its construction site in Frankston from 6am to 3pm before making a trip to Box Hill Action Indoor Sports from 7.30pm for two hours last Wednesday.

The confirmed case returned to the same auto dealership on Thursday and Friday between 6am and 3pm both days.

In Brisbane, another person who was likely infectious visited The Village shopping centre in Upper Mount Gravatt on Thursday.

The person made a stop at the Subway store between 3pm and 3.45pm before walking across to Coles from 3.15pm to 4pm.

On Monday, the same person visited Good Price Pharmacy Warehouse in Mount Gravatt between 1.30pm and 3.30pm before going to Princess Alexandria Hospital's emergency department from 3.15pm to 6.45am the next day.

Anyone who attended any of the exposure sites on the specific dates and times should monitor for symptoms of measles which can include fever, cough, sore or red eyes, runny nose, and feeling generally unwell, followed by a red bumpy rash.

However, NSW Health's Dr Christine Selvey says the locations pose no ongoing risk.

Unvaccinated babies are at high risk of contracting the virus while infants, pregnant women and people with weakened immune systems are at an increased risk of serious complications, including pneumonia and brain inflammation.

Symptoms can develop between seven to 18 days after exposure with people warned to be vigilant as initial symptoms may be similar to COVID-19 or the flu.

"If a symptomatic person tests negative for COVID-19 and/or influenza but develops a rash, they should be advised to continue isolating and be tested for measles," Dr Looker said.

People are potentially infectious from 24 hours before experiencing symptoms until four days after the rash appears.

The virus can spread through airborne droplets or contact with nose or throat secretions and contaminated surfaces and objects, lasting for up to two hours in the environment.

Measles outbreaks have recently been reported in Asia, Africa, Europe, the Middle East and the USA.