In its attempts to keep the virus out, China’s continued to prohibit crew changes for foreign crew and recently imposed as much as a seven-week mandatory quarantine for returning Chinese seafarers. Even vessels that have refreshed their crew elsewhere have to wait two weeks before they’re allowed to port in China.

To comply, shipowners and managers have had to reroute ships, delaying shipments and crew changes, adding to the supply chain crisis. “China’s restrictions cause knock-on effects,” said Guy Platten, the secretary general of the International Chamber of Shipping, which represents shipowners and operators. “Any restrictions to ship operations have an accumulative impact on the supply chain and cause real disruptions.”

The world’s biggest exporter, China is a key hub for the shipping industry. It is also the last country to hew to a Covid Zero policy, with increasingly radical measures. In recent weeks, authorities locked in 34,000 people at Shanghai Disneyland for mandatory testing. A Beijing school held primary school children overnight after a teacher tested positive. The definition of “close contact” now extends to people separated by as much as a kilometer.