The number of people with influenza in Canterbury surged and hospitals and health professionals are treating an increasing number of people with flu-like symptoms.
A spokesperson for Canterbury District Health Board says the sudden increase has brought the region's flu rate well above the national average, and it is urging people to get the flu vaccine.
The board says hospital admissions for flu rose from 23 people in May to 38 in June.
The DHB says the increase is not a result of any new strains of flu. Most cases have been identified as the seasonal strain but some cases of H1N1 and Influenza B virus have been diagnosed.
About 400 people die of complications from a flu-related illness in New Zealand every year.