Tokyo, Aug 16 (IANS): A food poisoning outbreak has affected 458 people over contaminated spring water in a restaurant in southwest Japan, local media reported on Friday.

The incident is linked to a restaurant in Yufu city of the southwest Japanese prefecture of Oita, where customers who dined or drank spring water between Aug. 3 and Aug. 12 experienced symptoms such as diarrhea and vomiting, Jiji Press reported citing local authorities.

The outbreak initially came to light on Tuesday, when 28 high school students from Tokyo reported symptoms after visiting the restaurant, according to Jiji.

The restaurant was ordered to cease operations for three days until Thursday, but further investigations revealed the number of affected individuals had expanded to 458 across 18 prefectures, Xinhua news agency reported.

The prefectural government announced that norovirus was detected in patients, raising concerns that the restaurant's spring water, used in food preparation, may have been contaminated.

Two people were briefly hospitalized but were not seriously ill, and all patients were reported to have experienced only mild symptoms.

An investigation is underway to determine the exact cause of the food poisoning.