The US state department has urged its staff in China to alert them to any abnormal hearing or vision issues after one employee reported mystery symptoms.
In a separate notice, the State Department said it's not aware of any similar situations in China, either inside or outside the diplomatic community.
In Cuba past year, the United States disclosed that 24 diplomats and their family members had fallen victim to an unsolved mysterious attack that left them with injuries resembling brain trauma. At least two Canadians were also affected. It didn't further identify the person with the symptoms or say when they had been detected.
Wednesday's alert said the US government does not know the cause of the reported symptoms and has not received similar reports in other parts of China, but that it is taking the report seriously.
The statement continues with a warning: "While in China, if you experience any unusual acute auditory or sensory phenomena accompanied by unusual sounds or piercing noises, do not attempt to locate their source".
For most the symptoms occurred around May 2017, but they were first reported in late 2016.
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"The (State) Department is taking this incident very seriously and is working to determine the cause and impact of the incident", US Embassy spokeswoman Jinnie Lee told Agence France-Presse.
It added the Chinese Government told the embassy it is also investigating and taking appropriate measures.
China's Foreign Ministry did not immediately respond to a request for comment.
The unnamed American citizen assigned to the consulate in Guangzhou had reported a variety of "physical symptoms" dating from late 2017 to April this year, the US embassy in Beijing said in an email.
In an emailed notice to American citizens in China, the department said it wasn't now known what caused the symptoms in the city of Guangzhou, where an American consulate is located. Previous victims of similar attacks in Cuba suffered permanent hearing loss, severe headaches, loss of balance, brain swelling, and disruption to cognitive functions.
Officials initially suspected the Americans had been targeted by an acoustic weapon, but media reports have suggested that the Federal Bureau of Investigation has been unable to verify any evidence to support that theory. Media reports have suggested that the Federal Bureau of Investigation has not been able to verify any evidence to support the sonic weapon theory.