A measles alert has been issued for the Brisbane and Sydney regions after a woman caught a train between the two cities earlier this month.

The woman arrived at Roma Street Station on April 6 and stayed in Highgate Hill. Metro South Health physician Dr Bhakti Vasant is calling for anyone with symptoms to report directly to a doctor, but to call ahead first to prevent further spread of the infection.

Anyone who is yet to be vaccinated for the measles, mumps and rubella vaccine is advised to visit their GP to receive a free vaccination.