At least 20 giant bulk carriers are anchored off the Chinese port of Jingtang and unable to offload millions of tons of Australian coal, the latest casualty of the growing diplomatic row between Canberra and Beijing.

Fifteen of the ships have been waiting since June, and the remainder have been delayed for at least four weeks, according to an analysis of shipping data conducted by Bloomberg. The northern port is one of the nation’s key gateways for metallurgical coal imports used in steel production.

The delays come as a political spat between the two countries escalates into a one-sided trade war, with China blacklisting commodities and foodstuffs from coal to lobster. Trade this year had also been ensnarled in virus measures amid port restrictions to halt the spread of COVID-19. A little more than 2 million tons of coal is held in the ships near Jingtang.