"China may be hoping to both send a message to other countries involved in the South China Sea that China will not back down under any circumstances, and send a message to a domestic population about the strong leadership of the party," she added.

'No rolling back' on China's part

The coronavirus, which has infected over two million people globally, first appeared in the Chinese city of Wuhan in December last year. There have been accusations both domestically and internationally that Chinese authorities ignored early warnings about the outbreak and attempted to downplay its severity. Collin Koh, an expert on maritime security at Singapore's Nanyang Technological University (NTU), told CNBC there were "speculations" about whether the pandemic would hamper China's ability to "maintain vigil over issues of national defense and security concerns." "This would send the wrong signal back home and to the international community — that there's a let-up in asserting such interests that concern sovereignty and rights," he said, explaining that could be why China has had to maintain its activity in the South China Sea. "What I observe is that, since the outbreak till present, there's no rolling back at all," said Koh, a senior fellow at the S. Rajaratnam School of International Studies, a think tank within NTU. Issues surrounding the South China Sea have for years been a point of contention in the relationship between the U.S. and China — the world's top two economies competing for geopolitical influence in Asia Pacific.

The U.S. doesn't claim any parts of the South China Sea as its own but has long promoted the "freedom of navigation" by air and sea across the waterway, which Washington has accused Beijing of militarizing. The U.S. has conducted activities including surveillance and military exercises in the area that is also a vital commercial shipping route, where an estimated $3.4 trillion of the world's trade passed through in 2016, according to think tank Center for Strategic and International Studies. Meanwhile, the U.S. Energy Information Administration (EIA) estimated that more than 30% of the world's maritime crude oil trade — or an estimated 15 million barrels per day — passed through those waters in 2016. Data by the EIA also showed that the South China Sea is rich in resources, containing some 11 billion barrels of oil and 190 trillion cubic feet of natural gas in proved and probable reserves can be found there.

Growing US-China mistrust

Following the sinking of the Vietnamese fishing boat, the U.S. hit out at China, saying it's "seriously concerned" by reports of what Beijing did. "This incident is the latest in a long string of PRC actions to assert unlawful maritime claims and disadvantage its Southeast Asian neighbors in the South China Sea," the U.S. Department of State said in a statement, referring to China's formal name, People's Republic of China. "We call on the PRC to remain focused on supporting international efforts to combat the global pandemic, and to stop exploiting the distraction or vulnerability of other states to expand its unlawful claims in the South China Sea," the statement read.

We don't need extraneous crises right now, we've certainly got enough on our plate with this once-in-a-century kind of global crisis that we're all facing right now. Susan Thornton senior fellow at Yale University's law school

In response, China's Ministry of Foreign Affairs accused the U.S. of sending "warships and planes to make waves in the South China Sea" and attempting to "negate China's legitimate claims and stir up troubles." "At present, the world is in a crucial period of jointly combating the pandemic. While fighting the pandemic at home, China is doing its utmost to support and help other countries in need, which has won universal praise from the international community," said a Chinese foreign ministry spokesman Zhao Lijian. "China urges the US to stop linking the pandemic with maritime issues and focus on domestic and international anti-epidemic response instead of doing otherwise," Zhao added.

Such an exchange could contribute to "a worsening relationship around foreign policy issues" between the U.S. and China, said Broderick of Eurasia Group. She added that in the coming weeks, the U.S. may be "especially sensitive to China's attempts to leverage its Covid-19 aid for more leadership in international institutions like the (United Nations) or for a stronger leadership role in Asia." Further mistrust between the U.S. and China is also unnecessary at a time when countries globally should be working together to fend off a fast-spreading coronavirus disease, said Susan Thornton, a lecturer and senior fellow at Yale University's law school. She told CNBC's "Squawk Box Asia" that both countries should focus on getting their respective economies back on track, and set aside "other issues that are still pending." "We don't need extraneous crises right now, we've certainly got enough on our plate with this once-in-a-century kind of global crisis that we're all facing right now," she said.

Territorial claims over South China Sea

Nevertheless, China's sinking of the Vietnamese fishing vessel in a part of the South China Sea claimed by both sides reflects the ongoing tensions among countries involved in a complicated and decades-long territorial dispute.

... my concern is that any of the claimants, China in particular, might simply use this window of delay to further consolidate and strengthen its position in the (South China Sea). Collin Koh Nanyang Technological University