Several school trips to Greymouth have ended in vomiting and diarrhoea for some students after a suspected outbreak of norovirus.

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The Canterbury District Health Board was contacted yesterday after 17 people from two different schools groups, staying at the same holiday park, got sick.

Nine Cashmere High School pupils fell ill on a geography field trip early last week.

A second group from the same school began their field trip a few days later and a further two fell ill as well as one adult.

A group of 40 Ohoka Primary School children were also staying at the holiday park and seven came down with the same vomiting and diarrhoea.

Canterbury Medical Officer of Health Cheryl Brunton said while they had been unable to do testing yet the rapid spread would indicate a viral gastroenteritis.

"The most common form of gastroenteritis is norovirus so we're making the assumption that that is the cause of this outbreak....it's behaving that way so we're giving advice on that basis."

She said while it could often be caught through contaminated food or water, it was likely just one student was exposed to it and the illness cascaded from there.

"The disease is unfortunately very highly infectious and we often get outbreaks in what we call an institutional setting, so things like schools, resthomes, and in this particular case children in relatively closer quarters than they might ordinary be.

"One child vomits, there's enough virus particles to infect the others just in the same room."

Dr Brunton said they had contacted the schools involved and provided advice to parents.

"Unfortunate some children, particularly from that last group, weren't able to take their much anticipated trip home on the Trans Alpine train."

She said the holiday park had also been given advice, and the local council would be inspecting it to make sure everything had been cleaned and there was no further risk.

"You might think normal cleaning processes would deal with it but you actually need to do more including using bleach-based cleaners to make sure that you've actually got rid of any trace of the virus."