BEIJING (News Nation) — Chinese officials in two separate cities say they have found traces of the new coronavirus in imported frozen food and on food packaging.

A sample taken from the surface of frozen chicken wings imported into the southern city of Shenzhen from Brazil, as well as samples of outer packaging of frozen Ecuadorian shrimp sold in the northwestern Xi’An city, have tested positive for the virus, local authorities said on Thursday

The discoveries came just a day after traces of the coronavirus that causes COVID-19 were found on the packaging of frozen shrimp from Ecuador in a city in eastern Anhui province. China has been stepping up screenings at ports amid the concerns over food imports.

Shenzhen’s health officials traced and tested everyone who might have came into contact with the potentially contaminated food products, and all results were negative, the city’s notice said.

The Shenzhen Epidemic Prevention and Control Headquarters said the public needed to take precautions to reduce infection risks from imported meat and seafood.

“It is hard to say at which stage the frozen chicken got infected,” said a China-based official at a Brazilian meat exporter.

The health commission of Shannxi province, where Xi’An city is located, said authorities are testing people and the surrounding environment connected to the contaminated shrimp products sold in a local market.

In addition to screening all meat and seafood containers coming into major ports in recent months, China has suspended some meat imports from various origins, including Brazil, since mid-June.

The first cluster of COVID-19 cases was linked to the Huanan seafood market in the city of Wuhan. Initial studies suggested the virus originated in animal products on sale at the market.

Neither the Brazilian or Ecuadorian embassies in Beijing have commented on the matter.