A top US-based expert on China has warned of "something worse" than COVID-19 if the United States does not take drastic action over the fungus smuggling case, media reports said.

The warning comes days after two Chinese scientists were charged with allegedly smuggling a toxic fungus into the US.

Yunqing Jian, 33, and her boyfriend Zunyong Liu, 34, allegedly conspired to smuggle into the US a fungus called 'Fusarium graminearum'.

The fungus has the potential to cause "head blight," a disease of wheat, barley, maize, and rice.

The US Justice Department said the fungus is classified in scientific literature as a 'potential agroterrorism weapon' and causes billions of dollars in losses each year.

It causes vomiting, liver damage, and reproductive defects in humans and livestock.

The couple had previously conducted work on the fungus in China.

Speaking on the case, America's top expert on Chinese affairs, Gordon G Chang, told Fox News that the couple's action amounted to waging war against the US.

Chang said that if the US does not take drastic steps like cutting off ties with China, it may be hit "perhaps with something worse" than Covid.

The origin of the novel coronavirus SARS-CoV-2, which caused the COVID-19 pandemic, is a matter of huge controversy, as some experts suspect the coronavirus was allegedly engineered in a Chinese lab.