There have been more than 155 outbreaks of highly infectious gastroenteritis in NSW childcare centres this month, nearly double the usual number of cases.

Richard Broome from NSW Health said almost 1000 children and more than 210 staff members had been affected in February, a 97 per cent increase for the month.

"Since then there have been further notifications of gastroenteritis outbreaks across the sector," he said on Thursday.

Viral gastroenteritis symptoms include nausea, vomiting, diarrhoea, fever, abdominal pain, headache and muscle aches.

The symptoms can take up to three days to develop and usually last between one or two days, or longer.

Parents and caregivers are advised to keep children home until 48 hours have passed from their last symptom.

Most people recover without complications but it can be serious for infants, people with suppressed immune systems and the elderly.