Several patients have been treated in Hawkes Bay Hospital as a result of contamination of the Havelock North town water supply.
"Two people were admitted to hospital overnight and a small number have presented to the emergency department this morning [and] GPs are seeing more," a Hawkes Bay District Health Board spokeswoman said today.
Two weeks' worth of bottled water has flown off supermarket shelves in less than 24 hours in Havelock North as the town battles the vomiting bug caused by the local council's water supply.
"We haven't run out of water. The customers have been running in since 5 o'clock last night. That's when we first got wind of it, which is not a lot of notice on a Friday night," David Findon, duty manager of New World, Havelock North's sole supermarket, said today.
"We sold out two weeks' worth of supply yesterday. We have got in five pallets of water this morning and it's pretty much all gone.
We've got another six pallets coming in at lunchtime." He said this would bring the tally to six months' usual supply.
The district health board and the Hastings District Council yesterday told Havelock North residents to boil water for one minute before consuming it, because of the outbreak of vomiting and diarrhoea.
The town's water supply has today been confirmed by the two agencies as the source of the outbreak of disease which, as well as an upset stomach, is causing headaches, muscle pain and fever. But how the contamination happened is unclear.
"I think there is a problem somewhere - we've had three of these [incidents] in the last year," said Hastings Mayor Lawrence Yule. "We don't know what the cause is. There's certainly a problem with those bore fields."
Medical officer of health Dr Nick Jones said the council chlorinated its water supply yesterday and this would kill most bugs but residents should continue to boil tap water before consumption until the bug causing the outbreak is identified. The results of tests for the bug are expected early next week.
The symptoms being experienced by those infected with the water-borne bug could last for up to 10 days, but would usually get better without antibiotics. Children and older people were most at risk of dehydration, and drinking fluids, while diarrhoea lasted, was very important.
One school reported 94 pupils were off sick with an upset stomach and a parent told the Herald that around the same number were off sick yesterday at another.
NZME staffer Belinda Henley, a mother of two who divides her time between Auckland and Hawke's Bay, said Havelock North was unusually quiet today.
"I'm in a cafe in Havelock and there's nobody here. It's my local cafe which on a Saturday you normally can't get a seat. It's amazing," said Henley, NZME's executive producer of video news.
"I've just been to my kid's hockey game. I reckon there was half the kids there normally are. It's quite freaky." Henley had been sick for three days with the local bug which, as well as the classic symptoms, had given her a fever and bad headaches.
Another Hawkes Bay mother of two, Ola Roberts, had a bad dose of gastro - and so did her kids.
"My daughter is the worst - she's got a high temperature, cramps, diarrhoea and she's not eating," Roberts said.
She said the most frustrating thing was that they'd all been drinking tap water to rehydrate - only to find that it could be the source of their woes.
"With the announcement, we've gone to bought water. I'm not sure I'm keen to risk drinking even boiled water." She said the outbreak was the worst she'd seen, in terms of how widespread it was.
"I coach football and half the team is unwell. I really hope that it passes through quickly and the council looks at ways to prevent it happening again."
The district health board last month reported that a stomach bug was widespread in the community. In one 24-hour period, six people were admitted to Hawkes Bay Hospital and more had turned up to its emergency department.
In September last year, low levels of e-coli were found in Havelock North's drinking water supply. The council chlorinated the supply and reported it may have been the heavy rain of preceding days that had led to a water supply bore being contaminated by stormwater.
In August 2012, 138 people fell sick with campylobacter gastro infection after heavy rain flushed animal effluent into the Darfield town water supply, according to a report by the Canterbury DHB.
An article in the New Zealand Medical Journal said the Darfield outbreak was "one of the largest outbreaks of waterborne disease ever recorded in NZ".
• Anyone with concerns can call Healthline on 0800 611 116 for advice from a registered nurse.
- additional reporting Susan Strongman