A Covid outbreak that has partially shut one of the world’s busiest container ports is heightening concerns that the rapid spread of the delta variant will lead to a repeat of last year’s shipping nightmares.

The Port of Los Angeles, which saw its volumes dip because of a June Covid outbreak at the Yantian port in China, is bracing for another potential decline because of the latest shutdown at the Ningbo-Zhoushan port in China, a spokesman said. Anton Posner, chief executive officer of supply-chain management company Mercury Resources, said that many companies chartering ships are already adding Covid contract clauses as insurance so they won’t have to pay for stranded ships.

It seemed as if things were just starting to calm down, “and we’re now into delta delays,” Emmanouil Xidias, partner at Ifchor North America LLC, said in a phone interview. “You’re going to have a secondary hit.”

The shutdown at Ningbo-Zhoushan is raising fears that ports around the world will soon face the same kind of outbreaks and Covid restrictions that slowed the flows of everything from perishable food to electronics last year as the pandemic took hold. Infections are threatening to spread at docks just as the world’s shipping system is already struggling to handle unprecedented demand with economies reopening and manufacturing picking up.

The Baltic Dry Index that serves as a global benchmark for bulk shipping prices is up more than 10% since a month ago as the delta variant began to spread rapidly. While there haven’t been significant effects on U.S. ports, the problems in China could hurt companies that rely on container exports from the nation.