HANOI: United States Vice President Kamala Harris landed in Vietnam Tuesday after an "anomalous health incident" in Hanoi delayed her flight from Singapore, the US embassy said, an apparent reference to the so-called "Havana syndrome" that has sickened diplomats in several countries.

Harris is in Vietnam as part of a Southeast Asia trip where she is seeking to rally regional allies as the United States' superpower status takes a hit over Afghanistan.

She was due to depart Singapore at around 4:00 pm (0800 GMT) Tuesday but her trip was delayed by around three hours.

"The Vice President's travelling delegation was delayed from departing Singapore because the Vice President's office was made aware of a report of a recent possible anomalous health incident in Hanoi," the US embassy statement said.

Harris senior advisor Symone Sanders told reporters the delay "has nothing to do with the Vice President's health".

The US is still unsure of what causes the so-called "Havana syndrome" five years after the first case in Cuba when US diplomats and their families complained of nosebleeds, migraines, and nausea after experiencing piercing sounds at night.

Since then, similar complaints have been reported by US officials in China, Russia, and inside the United States.

The problem has led to unproven allegations that Russians or others used sonic or other high-intensity electronic devices to physically harm US diplomats.

Harris' Vietnam trip comes as Washington seeks to reset relations in Asia after the turbulent Donald Trump era and build a bulwark against the rising might of Beijing.

On Tuesday, she accused China of intimidation in disputed Asian waters.

But her trip to the region, which also includes a stop in Vietnam, comes as Washington faces fresh questions over its dependability amid the US pullout from Afghanistan and Taliban takeover.