Health officials are urging parents to ensure their children are immunised against whooping cough after a spike in diagnoses of the disease in northern New South Wales.

Northern New South Wales Public Health Unit acting director Greg Bell said there had been 37 reported cases in the past week, which was double that of the previous week.

"A week ago we had 15 cases, which is drifting along to what we would expect, then all of a sudden it doubled up to 37 cases and this week we are looking quite high again," Mr Bell said.

"It is a spike that adds concern to us for protecting our little ones, unvaccinated and little ones that haven't started vaccinations."

Northern New South Wales has some of the lowest vaccination rates in Australia, which the public health unit's immunisation coordinator Marianne Trent said was concerning.

"Whooping cough is not called the 100-day cough for nothing," Ms Trent said.

"If you are unvaccinated and you get whooping cough, you can expect to cough for 100 days.

"It is very disruptive if you are a child, but it's not likely to kill you as it is [with] babies."

Outbreak at Ballina school

At least six students at the Teven-Tintenbar Public School near Ballina have been diagnosed with whooping cough since April 13.

Lani Clarke is the mother of two girls who attend the school and have been diagnosed with the disease.

She said the school contacted her to say her six-year-old daughter had a cough, then advised her to seek medical attention.

"The next day I took her to be tested, and the results came back in two-and-a-half days saying she has it," Ms Clarke said.

"You know, she wasn't sick, other than a chesty cough that we all get at this time of year."

Ms Clark said both her daughters were vaccinated and their coughs did not have a distinctive whooping sound.

"Just the same cough you have when kids are rundown, a chesty cough," she said.

Mother concerned about young family members

Ms Clarke said she had to contact relatives they were visiting in Sydney during the school holidays to let them know her daughter had tested positive to whooping cough.

"So, this sister from the North Coast might have taken her whooping cough down to Sydney," she said.

"One of my sisters has a four-month-old and an 18-month-old, so I am feeling terrible calling them … and my other sister is pregnant.

"They are waiting for results at the moment."

A sports carnival to be hosted by Teven-Tintenbar Public School will still go ahead tomorrow.

Mr Bell said the school had received advice from health officials about hosting the event and the potential risk.

"Our group has been having discussions with the host, the school, and it would be prudent that they do let people know," he said.