Sydney parents are urged to be aware of the symptoms of whopping cough, with health authorities confirming an outbreak across parts of New South Wales.
There's been 2,800 cases in Sydney this year, with 300 already this month.
Dr Vicki Sheppard from NSW Health says if children develop cold or flu like symptoms, it's best they visit their GP.
"A cough develops that's often worse at night and comes in bouts, particularly in un-vaccinated people," she told the Hit Newsroom.
"The bouts of coughing can be followed by vomiting, or a loud sound, which is called the 'whoop'."
Dr Sheppard said the outbreak is also a reminder for all pregnant women to be vaccinated.