A measles alert has been issued after NSW Health was notified about a woman with the infectious disease in western Sydney.

There is no ongoing risk to the public, but Western Sydney Local Health District public health unit acting director Conrad Moreira said people who potentially had contact with the woman should monitor for symptoms.

"Symptoms include fever, sore eyes, runny nose and a cough followed three or four days later by a red, blotchy rash that spreads from the head to the rest of the body," Dr Moreira said in a statement.

Potential contacts included people who visited Baby Bunting at Blacktown Megacentre and Kmart Blacktown on March 24 between 3pm and 5pm, Winston Hills Mall on March 28 between midday and 2.30pm and Westmead Hospital Emergency Department on March 29 from 2pm to 10.30pm.

Measles is spread through the air via coughs or sneezes from infected people, and symptoms can take up to 18 days to appear after exposure.

"Anyone who develops symptoms should see their GP and call ahead to make sure they are not put in the waiting room with other patients," Dr .

The disease can lead to respiratory or neurological complications in young children or older patients, and in pregnant women can cause low birth weight or premature birth.

"Measles is highly infectious and anyone born during or after 1966 needs to make sure they have received two doses of measles vaccine to be properly protected," Dr Moreira said.

Vaccination is safe and very effective, she said.

"Two doses of measles-mumps-rubella vaccine provide lifelong protection against measles."

Free measles vaccine is available in NSW to anyone born during or after 1966 who doesn't have two documented doses of measles vaccine.