More than $500 million worth of Australian coal is on ships anchored off Chinese ports, as a diplomatic spat between the two countries cuts into trade, idles a portion of the world’s dry bulk carriers and threatens to spiral into a humanitarian crisis. More than 50 vessels have been waiting a month or longer to offload coal from Australia, according to separate analyses of shipping data conducted by Bloomberg and data intelligence firm Kpler. There’s about 5.7 million tons of coal and approximately 1,000 seafarers on the anchored vessels, which are mostly Capesize and Panamax-sized vessels, according to Kpler.

The cargo and crew are victims of China’s move to blacklist a wide swathe of Australian commodities and foodstuffs, ratcheting up tensions between the two trading partners that have deteriorated since Huawei Technologies Co. was barred from building Australia’s 5G network in 2018. Chinese power stations and steel mills were told to stop using Australian coal and ports were instructed not to offload the fuel, Bloomberg News reported in October.

Recent trade measures taken by China were made to protect public health and are consistent with World Trade Organization obligations, Wang Xiaolong, director-general of the Ministry of Foreign Affairs’ International Economic Affairs Department, said Monday in Beijing.