An unvaccinated baby has contracted measles after arriving in Sydney, prompting pleas from the health department for people to get the jab.

The infant, which was travelling from South East Asia, came down with the potentially deadly infection last week shortly after arriving in Sydney.

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The child visited major tourist attractions including Circular Quay, Taronga Zoo and Chinatown as well as Canberra, Jindabyne and Perisher between August 17 and 19.

NSW Health's communicable diseases director Vicky Sheppeard urged people to ensure they were fully vaccinated and be wary of symptoms if they visited the same places as the infected child.

"The measles-mumps-rubella (MMR) vaccine is safe and highly effective protection against measles, and is available for free for those aged one to 52 from your GP," she said in a statement on Thursday.

"If you are unsure whether you have had two doses, it is quite safe to have another dose."

More than 94 per cent of five year olds in NSW are vaccinated, the highest levels ever, NSW Health said.

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But the disease is highly contagious and spreads through the air when infected people sneeze or cough.

"Vaccination is your best protection against this extremely contagious disease," Dr Sheppeard said.