A second measles warning has been issued for Sydneysiders who may have come into contact with two infected children on a flight into the city.

Two unvaccinated children with measles have flown into Sydney from Sri Lanka prompting a health warning over the contagious virus.

NSW Health on Tuesday issued a warning to people who were on flight SQ221 from Singapore which arrived in Sydney on January 11.

Two children on the flight were diagnosed with measles on Tuesday.

The children caught the train on January 11 from the International Airport to Meadowbank via Central.

People who may have come into contact with the children have been warned to be alert for symptoms until late January.

"If you develop symptoms please call ahead to your GP so that you do not wait in the waiting room with other patients," communicable diseases director Dr Vicky Sheppeard said in a statement.

The warning comes a day after another airport measles scare involving a man who flew into Sydney from Manila on January 11.

Vaccination rates for five-year-olds have increased from 88 per cent to 95 per cent between 2010 and 2017.

Symptoms of measles include fever, sore eyes and a cough, followed three or four days later by a red, blotchy rash, NSW Health says.