Tainted tap water has sickened hundreds of people in a small town on New Zealand's North Island and forced schools to close.

Health officials said Monday that 21 people in Havelock North have been hospitalized, including two in critical condition, after testing positive for campylobacter bacteria.

The bacteria are typically spread from animal feces. Officials say they don't know yet know how the underground water aquifers that supply the town became contaminated.

Officials said they have been treating the water with chlorine since Friday and are urging residents to boil tap water.

Five local schools decided to close for the next two days, saying about half the children were sick as well as many teachers.

About 13,000 people live in Havelock North. The region is known for its vineyards.