Farmers are illegally growing genetically modified corn in China’s northeast, said environmental non-profit Greenpeace on Wednesday, in a report that may generate further distrust of the government’s ability to ensure a safe food supply.

Beijing has spent billions of dollars to develop GMO crops that it hopes will ensure food supplies for its 1.4 billion people but has not yet approved commercial cultivation amid deep-seated anti-GMO sentiment. The new findings seem to confirm concerns that Beijing will be unable to supervise the planting of GMO crops once commercial cultivation is permitted, leading to widespread contamination of the food chain with GM varieties.

In its report, Greenpeace said 93 percent of samples taken last year from corn fields in five counties in Liaoning province, part of China’s breadbasket, tested positive for GMO contamination.

Furthermore, almost all of the seed samples taken from grain markets and samples of corn-based foods at supermarkets in the area also tested positive.

“It is very likely that much of the illegal GE corn has already entered grain storage warehouses, wholesale and retail markets across the country, ultimately ending up in citizens’ food,” said Greenpeace in a report.

While Greenpeace said it was not clear how the GMO corn seeds got into the marketplace, it has long been alleged that GMO plants being tested in field trials have been illegally sold to farmers for commercial use.

Such reports have intensified public opposition to the technology, with some anti-GMO campaigners going as far as suing the government over the failure to disclose information about its approvals for imported GMO crops and plans to allow domestic cultivation.

Among the six corn seed strains that tested positive in the Liaoning seed market, three have not been certified by China’s agriculture ministry, while three others were certified as conventional seeds and therefore had been contaminated by GMO varieties, said the organization.

The agriculture ministry did not immediately reply to a request for comment on the Greenpeace report.

The ministry said last year it was changing regulations to increase supervision of biotech products under development.

The GMO corn strains identified in the survey belong to international companies Monsanto, Syngenta and Du Pont Pioneer, said Greenpeace. None of the companies responded to emailed requests for comment.

Greenpeace blamed an “extremely lax and disorganized” seed market management system for the production and sale of illegal seed varieties.

It said many small seed breeders are not aware of the names of seeds they are breeding on behalf of other companies nor whether the origins of the seeds are legal.

Greenpeace recommends that the government investigate all corn breeding companies and destroy illegal GMO seeds. Additionally, there should be annual inspections of crops in north China during the sowing season, and tougher supervision of GMO crop research and cultivation. It says farmers should be compensated for their losses if GMO crops are destroyed.

The new findings could make Beijing even more cautious about proceeding with commercialization of any GMO crops, frustrating international and domestic seed firms.

Proponents of biotech crops in China argue that commercializing GMO products will reduce the need for farmers to resort to unapproved varieties to boost their yields.