Parcels posted from overseas may have spread the Omicron variant of the coronavirus in Beijing and elsewhere, Chinese state media has said.
The State Post Bureau said it has ordered stronger measures to ventilate and disinfect sites where items mailed from overseas are handled.
Postal workers must wear protective equipment, receive booster shots and undergo regular testing, it said on its website.
International packages must be isolated, cleaned and held for a waiting period to ensure they are free from the virus, it added.
The World Health Organisation says coronaviruses “need a live animal or human host to multiply and survive and cannot multiply on the surface of food packages”.
However, China has repeatedly emphasised what it calls the danger of infections from packaging, despite only trace amounts of the virus being found on such items, and has boosted testing of frozen food and other items shipped from overseas.
The Communist Party newspaper Global Times cited the Beijing Centre for Disease Control and virologists as linking recent infections to packages from abroad.
It said on Tuesday that investigators found people newly infected had picked up packages mailed from Canada and the US.
China has locked down parts of Beijing’s Haidian district following the detection of three cases, just weeks before the capital is to host the Winter Olympic Games.
Another person in the southern technology hub of Shenzhen who tested positive for Omicron handled packages sent from North America, the newspaper said.
China remains on high alert for new outbreaks ahead of the Olympics. Around 20 million people are under lockdown and mass testing has been ordered in entire cities where cases have been discovered.
Beijing Games organisers announced on Monday that only “selected” spectators will be permitted at the events, which officially open on February 4.
Beijing had already announced that no fans from outside the country will be permitted and has not offered tickets to the general public.
China has largely avoided major virus outbreaks with lockdowns, mass testing and travel restrictions, although it continues to fight surges in several cities, including the port of Tianjin, about an hour from Beijing.
One city that has endured weeks of lockdown under China’s “zero-Covid” policy appears to have received some relief.
Falling numbers of cases in Xi’an, a city of 13 million famed as the home of the Terracotta Warrior statue army, have prompted authorities to gradually allow people to leave their homes and return to work.
Just one additional case was reported in the city among China’s 127 new domestically transmitted cases announced on Tuesday.