Authorities said the popular fermented cabbage dish had been distributed to those now sick through school meals in the city. They added that students and staff from 24 schools were among the patients with vomiting, diarrhoea and abdominal pains.

Norovirus is very contagious and can be caught through touching contaminated surfaces – such as toilet flush handles – and from people who are already infected. Most people recover in a few days without needing hospital treatment, but some become very ill.

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Namwon City officials said it began an epidemiological investigation to uncover the source of the illness on Wednesday, after the first case was reported the previous day.

Since then, the number of cases grew rapidly – rising from 153 on Wednesday to 745 on Thursday. In a social media post on Thursday, the city’s Mayor, Choi Kyung-sik, said that health officials had adopted a “pre-emptive and excessive response” in an attempt to prevent further spread of the illness.

“We will ensure the safety of our citizens,” he added. City officials said norovirus had been detected among patients, through environmental samples and in some of the kimchi regularly delivered to schools.

As a result, its disaster and safety department had temporarily suspended the production and sale of any products from the company that made the kimchi – which is also in the process of voluntarily recalling products that have already been distributed.

The firm that produced the kimchi has not yet been officially named.