The child, whose gender and age have not been released, died in hospital, where several children from Little Zak's Academy in Artarmon have been recuperating.

Northern Sydney public health director Michael Staff said six children who attended the same childcare centre had been infected by rotavirus gastroenteritis over the past week.

Aged between 11 months and four years, four of the children were admitted to hospital after developing high fevers and vomiting.

Two of them had fully recovered and since been discharged.

"Tragically, another child who also attends the centre died in hospital on 23 October, but at this stage it appears unrelated to the gastroenteritis outbreak," Dr Staff said.

"The Public Health Unit is working with specialist paediatricians to understand the cause of death."

Managers of the childcare centre were working with the Northern Sydney public health unit to ensure appropriate measures were taken to avoid the spread of infectious illnesses and parents had been given information and advice, he said.

Little Zak's Academy released a statement on Wednesday evening offering condolences to the family.

"Everyone at our Artarmon Centre has been deeply saddened by this news and our directors have been in contact with the family of the child to offer our sincerest thoughts and condolences and to offer any support we can," the statement said.

"Please be assured our Artarmon centre is fully accredited and compliant with all health and regulatory requirements, and we endeavour at all times to operate to the highest standards of care and hygiene.

"As confirmed by Northern Sydney Health, we will continue to work closely with its Public Health Unit to ensure these high standards are maintained."

The public health unit had confirmed it was safe for children to continue to attend the centre, the statement said.

NSW Health has received 22 notifications of rotavirus in the week ending October 16 and 414 notifications this year, which is 200 less than this time last year.

Gastroenteritis, which is marked by vomiting, diarrhoea and stomach pain, is a common disease in children, but outbreaks are usually more prevalent in the winter months.

Rotavirus is the most common cause, and almost all children have been infected by the virus by the time they reach the age of five.

It is spread through contact with the vomit or faeces of an infected person, either directly or on contaminated objects, and symptoms typically occur two days after exposure.

Death from the virus is rare, but hospitalisations are common, particularly among children aged under two.

Parents at the centre told Channel Nine that children affected in the recent outbreak had been sick for seven days.

This winter saw a particularly severe strain of norovirus gastroenteritis, with 98 outbreaks in childcare centres and aged care centres in the months of June and July.

Fairfax Media has contacted the centre for comment.