An alert has been issued after two people who returned from overseas with measles visited several locations in Sydney while infectious.

NSW Health has declared multiple premises exposure sites after the two confirmed cases, from the same family, visited them between July 14 and Thursday.

Dr Anthea Katelaris, from South Eastern Sydney Public Health Unit, said anyone who was in the same locations as the cases should check their vaccination status and be alert for signs and symptoms of measles until August 7.

The confirmed cases visited locations including Sydney International Airport on July 14, a Rose Bay chemist on July 15, the Prince of Wales Hospital on Wednesday, and a bank and various shops in Randwick on Thursday.

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

Symptoms include fever, sore eyes and a cough followed three or four days later by a red, blotchy rash which typically spreads from the head and neck to the rest of the body.

It can take up to 18 days for symptoms to appear after exposure.

Anyone born in or after 1966 who has not received two doses of measles vaccine is advised to get a measles vaccine to prevent the infection.

"The measles-mumps-rubella vaccine is safe and effective protection against measles," Dr Katelaris said.

The vaccine is free for anyone born during or after 1966 who hasn't already had two doses.

Anyone who develops symptoms is advised to call a GP or medical centre ahead to ensure they can be isolated from other people.

Measles remains common in many parts of the world, with large outbreaks currently occurring in a number of locations.

Measles has also been reported in other states in recent weeks.