A dozen samples of fresh papaya - including four in Hong Kong - have been found to be genetically modified in tests by Greenpeace in the city and on the mainland.
Two of the local samples were from ParknShop supermarkets in Mong Kok and Ma On Shan, and two were from wet markets, Greenpeace said. The tests were part of an investigation by Greenpeace in 12 supermarkets and wet markets in Hong Kong, Beijing, Shanghai, Guangzhou and Shenzhen between February and March.
Thirteen samples of papaya were tested and only one, imported from the Philippines, was found not to have been genetically modified. All the others were produced on the mainland, mostly in Guangdong and Hainan provinces.
The environmentalist group said the genetic modification of food products was potentially damaging to consumers' health.
'Although the exact health risks of genetically engineered food remain unknown, some scientists have pointed out that people may become allergic to genetically modified papayas,' Greenpeace's food and agriculture campaigner, Lorena Luo Yuan-nan, said.
'They are also potentially harmful to people's immune system and their reproductive system.'
The group also went to Hainan to check three big papaya orchards in the region, where genetically modified papaya production is illegal.
'But all the samples from the orchards tested positive for genetic engineering,' Ms Luo said.
Greenpeace called on the central government to halt the sale and cultivation of genetically modified papayas and find out where they were coming from.
'We also want to call for the Hong Kong government to enhance regulation on the import of genetically modified products and all supermarkets to take tighter control when sourcing food from overseas,' Ms Luo said.
The sale of genetically modified foods is allowed in Hong Kong if it is deemed to be suitable for consumption under the Public Health and Municipal Services Ordinance.
A spokeswoman for the Food and Environmental Hygiene Department said the department was investigating Greenpeace's claims.
A ParknShop spokeswoman said the chain would not comment on any claims, as it had not received formal lab reports from Greenpeace. 'But we are sure that none of the papayas sold in our shops are from Hainan,' she said.