So far this year that have been 10 measles alerts issued to the public, with 12 people diagnosed with the disease in NSW since Christmas.

The most recent alert was after traveller arrived in Sydney and was diagnosed with measles after her flight.

The woman was infectious on flight number SQ231 which left Singapore Airport at 12.42 am on Tuesday, January 22 and arrived at Sydney International Airport at 11.58am on the same day.

The alert was for anyone who travelled on this flight, as well as those in Sydney International Airport around lunchtime on this date, including baggage carousels, customs and the arrivals area.

They are advised to be alert for signs and symptoms of measles until February 9.

The time from exposure to the onset of symptoms is from a week to 18 days.

Measles is highly contagious and is spread in the air through coughing or sneezing by someone who is unwell with the disease.

NSW Health communicable diseases branch director Dr Vicki Sheppeard said people should call their GP straight away if they develop signs.

She said outbreaks of measles in popular tourist destinations meant the risk for measles being imported into Australia at the moment was high.

She urged anyone travelling to South-East Asia, where measles is prevalent, to ensure they were fully vaccinated before heading overseas.

“The measles-mumps-rubella vaccine is safe and effective protection against measles,” Dr Sheppeard said.

“It is free for anyone born during or after 1966 who hasn’t already had two doses. If you’re unsure whether you’ve had two doses, it’s quite safe to have another.”

The main symptoms of measles include:

Followed three to four days later by a non-itchy, spotty rash that starts on the face and neck and spreads to other parts of the body.