The U.S. State Department is warning U.S. citizens in China that a government employee reported unusual "sensations of sound and pressure" and was later diagnosed with a mild traumatic brain injury - a case that recalls a wave of so-called "sonic attacks" on U.S. diplomats in Cuba.
The unusual incident recalls a similar spat of reports from Cuba, where USA officials reported symptoms consistent with a "sonic attack", or exposure to harmful frequencies, while overseas.
"We do not now know what caused the reported symptoms and we are not aware of any similar situations in China, either inside or outside of the diplomatic community", the State Department warned in a health alert.
The embassy's statement provided no details regarding the location where the incident was registered, however, the contacts of the US Consulate General in the southern Chinese city of Guangzhou were attached to it.
The unnamed employee in the city of Guangzhou "recently reported subtle and vague, but abnormal, sensations of sound and pressure", the State Department said in an emailed statement to U.S. citizens in China.
The employee working in Guangzhou, whose symptoms of "subtle and vague, but abnormal, sensations of sound and pressure" lasted from late 2016 through to April 2018, had been sent to the United States for medical evaluation.
"The embassy learned that the clinical findings of this evaluation matched mild traumatic brain injury", Lee said. The employee was sent back to the United States for assessment.
"We can not at this time connect it with what happened in Havana, but we are investigating all possibilities", a USA embassy official said.
The US official at the consulate in Guangzhou experienced a variety of "physical symptoms" between late 2017 and April this year.
Though the State Department has not linked this case to any other incident, news of unusual symptoms hitting US government employees overseas will no doubt draw comparison to a rash of incidents with USA and Canadian diplomats working in Cuba.
The still-unexplained incidents sparked a rift in US-Cuban relations, while investigators have considered theories including a sonic attack, electromagnetic weapon or flawed spying device.
An American flag is flown next to the Chinese national emblem during a welcome ceremony for visiting US President Donald Trump outside the Great Hall of the People in Beijing on Nov 9, 2017.
The diplomats described concussion-like symptoms like hearing loss, dizziness, balance problems, visual complaints, headaches, fatigue, cognitive issues and difficulty sleeping.
"The cause (of their symptoms) remains unknown but could be human-made", the Canadian government concluded.