A stomach bug that ripped through a University of Auckland residence has left 165 students sick, with the worst-affected needing hospital treatment.
Health chiefs have launched an investigation into the outbreak that erupted after a Hunger Games party at the 442-bed University Hall complex on Whitaker Place.
Students first started feeling queasy last Thursday afternoon and by Friday night dozens were dashing to the toilet.
"One girl started throwing up and couldn't quite make it to the bathroom and threw up in the shower. It was really bad," law and arts student Leina Barke said.
"I don't know where it came from but one night everyone just started throwing up and it just carried on for the whole weekend."
Barke started feeling sick on Friday and threw up three times that night, but was feeling much improved the next day.
Others weren't so fortunate. About 20 students sought treatment at Auckland City Hospital, with emergency department clinical director Dr Anil Nair saying most had mild dehydration. The worst affected, a group of about 12, were treated "for a few hours with intravenous fluids and antiemetics".
The 13-level hall houses students, mostly in their first year of university study, in single bedrooms with shared toilet facilities and common rooms. They also eat from the same canteen.
Some cases were also reported at the nearby Student Apartments, and the Grafton and Whitaker Halls.
"My floor was pretty bad," Barke said. "We had to separate the sick-people bathroom from the well-people bathroom."
The students had been taking part in a week-long activity based on The Hunger Games, where you "kill" opponents by squirting them with water or throwing a sock at them.
Music student Siyu Sun said one theory was the increased interaction may have helped the illness spread.
She didn't get sick but had seen people carrying bowls wherever they went.
The Auckland Regional Public Health Service said laboratory results indicated norovirus was the cause of the mass illness. Symptoms include nausea, vomiting, stomach cramps, headaches, chills, aching muscles and diarrhoea.
During the week the service had worked with various student bodies to manage the outbreak.
Although at least 20 people had sought hospital treatment, the service was not aware of any overnight admissions.
An investigation was ongoing into how it was introduced and spread.
"With this sort of outbreak people may become infected when they come into contact with contaminated food or surfaces, although it could also be spread in the air from things like vomiting or flushing of the toilet," the service said in a statement.
The students said facilities were always clean and well-managed.