WASHINGTON -- A new medical mystery affecting U.S. diplomatic workers, this time in China, is deepening. The U.S. Embassy in Beijing has issued two warnings for Americans in the country to watch out for unexplained illnesses.

Several workers at U.S. consulates in China have been evacuated after complaining of hearing odd sounds, then becoming ill. CBS News Radio's Steve Dorsey was first to report on similar ailments among U.S. government employees stationed in Cuba.

Dorsey reports that early Friday morning, the U.S. Embassy in Beijing issued its second health alert, urging Americans with "unexplained physical symptoms" to get medical help, as concerns grew that the mysterious case could be worse than first reported.

Diplomatic security officer Mark Lenzi is one the latest Americans to have been evacuated from the U.S. Consulate in Guangzhou, southern China.

He's back in the U.S. for treatment after he says he was injured after hearing odd sounds. In a statement to CBS News, Lenzi said the ordeal has been "stressful" for his family.

An undated photo provided by Mark Lenzi shows the U.S. State Department employee in Guangzhou, China. Mark Lenzi

Sen. Jeff Flake said Thursday that the State Department was "trying to work through it" and it was "obviously" concerned "about the health and safety of its diplomats."

In a similar case last year, 24 government employees and spouses at the U.S. Embassy in Cuba complained of headaches, ear pain, sleep impairment, and cognitive problems after saying they had heard strange sounds.

The U.S. retaliated by expelling Cuban diplomats.

On Tuesday, Secretary of State Mike Pompeo set up a medical task force to seek answers to the mysterious ailments. He addressed congress last month after the latest incidents in China were first reported, saying State had "medical teams that are moving to be on the ground there. We are working to figure out what took place."

The U.S. requested Chinese assistance in its investigation, but on Thursday, a Chinese Foreign Ministry spokesperson said China had conducted a thorough investigation of its own, and found nothing.

David Rank, the former deputy chief of mission at the U.S. Embassy in Beijing, said if there is an "implication or evidence that this was a state organized activity," it would have a "much bigger impact on our relations."

Lenzi told Dorsey this week that he'll soon begin treatment at the University of Pennsylvania. He's also calling on several top State Department officials to resign: accusing them of a cover up.