Whooping cough infections are continuing to rise across New South Wales, prompting urgent warnings to get vaccinated.
Notification levels of the infection have reached over 12,000 between January and September this year, the highest level since 2016, according to NSW Health.
The illness starts like a cold, with a blocked or runny nose and the occasional cough, NSW Health said.
Then, coughing will begin to worsen and can be followed by vomiting, choking or big gasping breaths, which causes a "whooping" sound.
The cough can last many weeks and gets worse at night.
In newborns, the coughing may not start at all, rather, they just stop breathing completely and start turning blue.
Other babies will have difficulty feeding, causing choking or gagging.
Pregnant women, parents, grandparents, and anyone in close contact with babies are being urged to get vaccinated to protect children against the severe, and sometimes deadly illness.
Vaccination during pregnancy is extremely important to help protect newborn babies, who are at the highest risk of serious illness from whooping cough, according to the NSW Health's Director of Communicable Diseases, Dr Christine Selvey.
"Pregnant women are recommended to be vaccinated between 20 and 32 weeks of every pregnancy as this enables whooping cough antibodies to be transferred to their unborn baby," she said.
"Parents and carers should ensure all children are vaccinated on time, especially in the first six months of life.
"It's also important all people in contact with newborn babies have had a pertussis vaccine within the previous 10 years.
"People aged five years and over can receive pertussis vaccination from GPs, pharmacist immunisers, and Aboriginal medical services.
"While notifications are increasing in all age groups, cases are highest in school-aged children."
A person with whooping cough will not be contagious after five days of prescribed antibiotics, however, without proper treatment they will remain infectious for 21 days.
"If given early, antibiotics can reduce the duration of symptoms," NSW Health said.
"Antibiotics are rarely needed if it has been three weeks since cough onset."
Free vaccines are available for pregnant women.
Anyone with symptoms should contact their GP early.
If a child is displaying life-threatening symptoms call triple zero (000) immediately.