Twenty-two people were ill with norovirus after a work Christmas party at an Upper Hutt restaurant in New Zealand.

Wellington medical officer of health Margot McLean said 22 of 39 people who dined at the restaurant last Saturday night all became ill between 10 and 50 hours after the meal.

Some vomited while others had diarrhea. Laboratory tests confirmed today the presence of norovirus.

She would not name the restaurant but said the diners were all in the same workplace party.

''Norovirus is spread from person to person and it was mostly caused by somebody who was ill, either a food handler or possibly somebody else, who spread it. We don't know for sure.''

She said this restaurant and all restaurants were advised to ensure food handlers who were ill with vomiting or diarrhea to stay off work for 48 hours.

''I guess the amount of these type of functions go up and its easier to identify outbreaks when this happens because there is a whole bunch of people who all come back and talk about it and ring Public Health.''