Harris, in Vietnam, gets a dose of Chinas challenge to the U.S.

Harris was en route Wednesday to announce, among other things, a donation of 1 million coronavirus vaccine doses to the pandemic-hit country. But a three-hour delay to her schedule handed China a window of opportunity.

Beijing quickly sent its envoy in Hanoi to meet with Vietnam's prime minister and pledged a donation of 2 million vaccine doses, undercutting the subsequent U.S. announcement. Prime Minister Pham Minh Chinh, thanking the envoy, said his country "does not ally with one country to fight against another," according to state media.

The incident underscored the challenges facing the Biden administration as Harris has made her way through Southeast Asia this week, along with Chinese sensitivity about her visit. Washington's agenda does not always align with that of governments in the region, which face a diplomatic high-wire act in balancing the competing interests of the United States and China - the latter being Vietnam's top trading partner.

"Beijing likes to remind Hanoi who of the two giants is closer to it," said Huong Le Thu, a senior analyst at the Australian Strategic Policy Institute.

Hanging over a trip intended to demonstrate a U.S. pivot to the Indo-Pacific has been the chaotic collapse of the Western-backed government in Afghanistan and resulting questions about Washington's commitment to its allies. China has seized on the turmoil to taunt the United States and label it an unreliable partner. But Beijing is also wary of American overtures to Vietnam, a fast-growing nation of 100 million with which it has competing territorial claims in the South China Sea.

Though Vietnam wants the United States to be stronger in resisting China's militarization of the disputed waterway, some in Vietnam's leadership would be hesitant to be seen as part of a Washington-led effort simply to counter their giant neighbor, Le Thu said.

For the second day in a row, Harris accused China of aggression in the South China Sea. Speaking at a bilateral meeting in Hanoi with Nguyen Xuan Phuc, Vietnam's president, Harris said there was a need to "raise the pressure" on Beijing's actions "and to challenge its bullying and excessive maritime claims."

Chinese Foreign Ministry spokesman Wang Wenbin, responding a question about Washington's support for Vietnam in the South China Sea, said the United States "arbitrarily launched military intervention in Afghanistan, Iraq and Syria, while claiming to defend the interests of smaller countries."

"I think it would be much more credible if the U.S. said it was trying to maintain its hegemony and uphold its own interests," he said.

Several countries claim overlapping territory in the resource-rich waters, a decades-long source of tension. An international tribunal in 2016 rejected Beijing's claims to an area demarcated by a nine-dash line, but China has asserted control by building up runways and other military installations on disputed islands, prompting an outcry from its neighbors.

The United States has contested the Chinese claims through freedom-of-navigation naval operations, noting the need to safeguard the billions of dollars in trade that flows through shipping lanes that connect East Asia with the Indian Ocean.

The vice president also spoke about upgrading the relationship between Vietnam and the United States to a "strategic partnership" and announced the donation of coronavirus vaccine doses, which she said would begin to arrive in the next 24 hours. She also laid flowers at a memorial in Hanoi to the late Sen. John McCain, who as a Navy pilot was shot down and captured by North Vietnamese forces during the Vietnam War.

In engagements across Singapore and Vietnam this week, Harris has pledged her country's commitment to the Indo-Pacific, which she labeled a "top priority" for the Biden administration. Analysts have seen her trip, particularly against the unfolding chaos in Afghanistan, as a way to prove the administration is refocusing on the region and on a broader strategy of countering China.

"Most partners across the region are happy to see the United States end its forever wars in the Middle East and finally prioritize Asia in the way that it has said it should for over a decade," said Greg Poling, a senior fellow for Southeast Asia at the Center for Strategic and International Studies. "Overall, it is likely to be a net positive for the administration, which it desperately needs right now."

Speaking in Singapore on Tuesday, Harris said Beijing "continues to coerce, to intimidate, and to make claims to the vast majority of the South China Sea" and "undermine the rules-based order."

Beijing hit back, noting - as Harris has - that countries in Southeast Asia do not want to be drawn into U.S.-China tensions and do not want to take sides. An editorial in the state-run China Daily said senior American officials who have visited the region want to "create a chasm" between China and Southeast Asian nations. The Global Times, also state-run, gloated that China's vaccine donation came before Harris's announcement.

Beijing's donation was made to the Vietnamese military, while the U.S. donation - bringing the total doses pledged so far to 6 million - is for the population at large.

After operating a successful containment strategy, Vietnam has faced a surge in coronavirus cases in recent weeks because of the more virulent delta variant. Ho Chi Minh City, the commercial hub, is under a strict lockdown enforced by the military. Soldiers are delivering food to residents.

Harris's arrival in Hanoi was delayed after the U.S. Embassy in Vietnam said it had detected a "possible anomalous health incident" in the city, a phrase that Washington uses to describe the Havana Syndrome. This refers to mysterious illnesses that have plagued dozens of U.S. government personnel, including diplomats at the U.S. Embassy in Havana in 2016.