Excessive amounts of aflatoxin were detected in five formula products made by Ava Dairy Co., Ltd. and its parent company during spot checks on Sunday in Guangdong province, said Li Yuanping, spokesman for China's General Administration of Quality Supervision, Inspection and Quarantine.

Li said authorities in Changsha, capital of Hunan province where the company is headquartered, have launched an investigation, and the company has started recalling the affected products.

According to Changsha's administration for industry and commerce, aflatoxin was found in 31.5 tonnes of products produced by the company between July and December last year. They were mainly sold to supermarkets in Hunan and Guangdong.

An initial probe indicated the contamination might have come from the feed.

Ava Dairy on Monday apologized on its website to consumers, promising an overhaul and cooperation with local officials in the investigation.

Aflatoxin is produced by a fungus that commonly grows on grain and peanuts. High levels of the toxin have been shown to cause cancer in animal tests.