An underground bore has tested positive for E.Coli and the Havelock North water supply chlorinated on Friday.
Iona College principal Shannon Warren issued a statement saying that due to the large number of girls and staff that were still ill, The Board of Trustees and Senior Management Team had decided to close the boarding house and the day school from 7.00pm tonight.
The boarding school will re-open on Tuesday evening for boarders and the day school will re-open Wednesday morning.
Ms Warren said the school was in a "unique situation" as the school was a residential facility with more than half of the students boarding.
Hastings District Council are on site flushing out water pipes to bring the chlorine through but the "boil water" notice was still in place.
"We understand that some families will be inconvenienced by this decision and we apologise for that but we do not apologise for prioritising the health and wellbeing of our staff and students," she said in the statement.
Woodford House was also closed until 4pm Tuesday, when boarders would be able to return, and Wednesday morning for the other students.
A few students who were unable to go home, including international students, would remain at the school.
In a statement, the school said "the health issues in Havelock North surrounding contaminated water have unfortunately affected a large number of girls and some staff.
"The Boards have considered this advice alongside the Ministry of Education guidelines and made the decision to close the school for two days. The wellbeing of our community is paramount."
This evening's final showing of the Lindisfarne College and Woodford House production The Lion King Jr had been postponed as a number involved were sick.
Accident and medical centres in the area have been seeing increased numbers of people with vomiting and diarrhoea today.
So far, 40 people have sought help from the Hastings Health Centre.
Hawke's Bay Hospital has two older people in its Intensive Care Unit in a critical condition, both with a gastro illness and both from Havelock North.
One was admitted today and the other on Friday, which initially seemed unrelated. The type of bug they have has not yet been determined but it now looks likely that both are related to the gastro outbreak in Havelock North.
Hastings District Health Board Medical Officer of Health Dr Nicholas Jones said gastroenteritis affected older and younger people much more severely and older people needed to seek medical help early on if they weren't getting better or couldn't keep fluids down. The same applied to young children.
He said they encouraged the community to keep an eye out for older people living alone.
The boil water notice for Havelock North residents' also remains in place today, however chlorination of the water supply seems to have been effective and is now throughout the Havelock North water supply.
Earlier today, Hawke's Bay Hospital reported more people presenting with vomiting and diarrhoea, with 15 people seen and one admitted.
Mr Jones said testing of sick people showed the majority of reported illness was caused by campylobacter.
Havelock North residents are advised to boil water despite the chlorination.
"The boil notice will remain until we are confident there is no other bug resistant to chlorination in the water, which is expected to take several days," he said.
Campylobacter could not be spread through air but could be if swallowed, so hand washing was "extremely important".
Hands needed to be washed thoroughly by using plenty of soap, cleaning under fingernails, rinsing hands well and drying on a clean towel: before and after preparing food, after going to the toilet or changing a baby's nappy, after caring for sick people and after touching animals.
Symptoms of the Havelock North illness were diarrhoea and influenza like symptoms: headaches, muscle pain, fever and feeling generally unwell.
Symptoms could last up to 10 days but would usually get better without antibiotics.
Gilmour Pharmacy and Denton's Pharmacy have opened today to provide more information and support for people.
Further advice for schools and early childhood centres would be distributed today.
Children and older people were most at risk of dehydration, while the diarrhoea lasted, so fluid intake was important.
For more information visit www.ourhealthhb.nz/assets/News-and-Event-files/HE1211-Campylobacter-WEB.pdf
People could also call Healthline on 0800 611 116 for around-the-clock advice from a trained registered nurse.
For information on the water supply contact Hastings District Council call 06 871 5000
