A US government employee in southern China has reported abnormal sensations of sound and pressure, the State Department said, recalling similar experiences among American diplomats in Cuba who later fell ill.
In an emailed notice to US citizens in China, the department said it was not currently known what caused the symptoms in the city of Guangzhou, where an American consulate is located.
“A US government employee in China recently reported subtle and vague, but abnormal, sensations of sound and pressure,” the notice said.
“The US government is taking these reports seriously and has informed its official staff in China of this event.”
The department said it was not aware of any similar situations in China, either within the diplomatic community or among others.
It did not further identify the person with the symptoms or say when they had been detected.
Despite hundreds of billions in annual trade between them, China and the US are considered strategic rivals for influence in Asia.
Tensions in the relationship frequently flare over accusations of cheating at trade, stealing of secrets, human rights and arms sales to Taiwan, a US partner that China claims as its own territory.
In Cuba, the US reported that some of its personnel and family members experienced a range of ailments, some after hearing an unusual sound.
For most, the symptoms occurred around May 2017.
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.
Symptoms, sounds and sensations reportedly varied dramatically from person to person.
Of the 21 medically confirmed US victims, some have permanent hearing loss or concussions, while others suffered nausea, headaches and ear-ringing.
Some felt vibrations or heard loud sounds mysteriously audible in only parts of rooms, and others heard nothing.