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.
US secretary of state Mike Pompeo, speaking in Washington to the House foreign affairs committee, said the medical indications of the incident in Guangzhou “are very similar and entirely consistent with the medical indications of the Americans working in Havana”.
He said a medical team was being sent to Guangzhou and “we are working to figure out what took place both in Havana and Guangzhou”.
State Department spokeswoman Heather Nauert said the US embassy learned on Friday that the Guangzhou employee had shown clinical findings during medical testing similar to patients with mild traumatic brain injury, known commonly as a concussion.
That is the same clinical finding that doctors treating the Cuba patients at the University of Philadelphia have found.
The Guangzhou worker started experiencing “a variety of symptoms” starting in late 2017, Ms Nauert said, adding that the symptoms continued through April.
The worker was sent to the US for additional testing.
On Monday, the US embassy in Beijing and all five of the US consulates in China held town hall meetings so that diplomats and embassy workers could ask questions or voice concerns.
Ambassador Terry Branstad led the session in Beijing.
Despite hundreds of billions of dollars 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, often 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.
Mr Pompeo said he expects the results of an independent investigation into the Cuban incidents by the middle of next week.
Last October, the State Department ordered non-essential embassy personnel and the families of all staff to leave Havana, arguing the US could not protect them from unexplained illnesses that have harmed at least 24 Americans.
Symptoms, sounds and sensations reportedly varied dramatically from person to person.
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.