Director North Coast public health unit Paul Corben says people who were travelling on the train at those times and who therefore may have been exposed to the two cases reported in the media earlier this week could still develop symptoms up until April 24 2019.

"We ask everyone to remain alert for symptoms of measles, and for people born during or after 1966 to take this opportunity to check their vaccination status and see their doctor for free vaccination if they haven't had two doses of the MMR vaccine," Mr Corben said.

On Friday April 5 a person now confirmed to have measles travelled while infectious on the 7.08am North Coast XPT from Sydney (Central) to Maitland, arriving at 10am.

On Saturday April 6 a second person who was infectious with measles caught the 7.08am North Coast XPT from Sydney (Central), transferred to the coach service 175 at Casino at about 7.10pm and arrived in Brisbane (Roma Street) at 9.45pm.

There are no known links between these cases.

Mr Corben said anyone who travelled on the North Coast XPT that left Sydney at 7.08am on either April 5 or 6 to any destination on the north coast or on the coach service between Casino and Brisbane on April 6 may have been exposed to the measles virus.

Anyone who develops symptoms should call ahead to their GP to ensure they're not in the waiting room with other patients.

Across NSW, 36 people have been infectious with measles since Christmas.

The latest annual immunisation coverage report shows vaccination rates in NSW are at their highest level ever, with more than 95 per cent of five year olds vaccinated against measles and around 92 per cent of five year olds on the north coast.

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

"NSW already has record immunisation rates but the community is not fully covered and measles is highly contagious and can stay in the air even after the person has left the room," Mr Corben said.

Symptoms of measles include fever, sore eyes and a cough followed three or four days later by a red, spotty rash spreading from the head and neck to the body.

Preventive injections can be given to highly-susceptible people up to six days after exposure to measles.

"The measles-mumps-rubella vaccine is safe and gives effective protection against measles," Mr Corben said.

"It's 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 safe to have another."

While the risk of infection is low in fully-vaccinated people, health experts urge anyone who comes into contact with someone who has measles to remain alert for symptoms. They should limit their exposure to others and seek medical care if symptoms develop.

Protecting children from potentially deadly diseases is a key priority for the NSW government, which has invested approximately $130 million in the 2018-19 Immunisation Program budget, including commonwealth and state vaccines.

For more information on measles visit the website.​