A seven-year-old NSW girl is critically ill in hospital after being diagnosed with tetanus, with the child reportedly not immunised against the potentially fatal disease.

The girl was initially treated at Lismore Base Hospital before being transferred on Wednesday to Brisbane's Lady Cilento Children's Hospital, health authorities say.

The bacterial infection, which can be transmitted from soil through a cut or wound, causes painful muscle spasms particularly in the neck and jaw and can lead to breathing difficulties.

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Lady Cilento Children's Hospital in a critical condition. Source: AAP

There is no cure and treatment focuses on managing the complications.

The ABC says the girl was not immunised against tetanus, which pro-vaccination advocates say is easily preventable.

Lady Cilento Children's Hospital on Friday said the girl's parents had asked for "complete privacy".

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A seven-year-old NSW girl is critically ill in hospital after being diagnosed with tetanus. Source: 7 News

The north coast region has some of the lowest vaccination rates in Australia.

Controversial anti-vaccination advocate David Wolfe on Thursday held a sold-out seminar in the nearby town of Mullumbimby.

Alison Gaylard, from the Northern Rivers Vaccination Supporters, criticised Byron Shire Council for allowing the controversial US speaker to use the Mullumbimby Civic Hall.

"It just seems tragic that while he could have been talking about his stance on vaccinations, there was an unvaccinated child being hospitalised with such an easily preventable disease," Ms Gaylard told AAP on Friday.

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