A United States Government employee in southern China has reported suffering from "abnormal" sounds and pressure leading to a mild brain injury, the U.S. embassy said - recalling similar experiences among American diplomats in Cuba.
The spokeswoman added that the Chinese government is also investigating the matter.
The embassy issued a health alert to U.S. citizens in China.
The Post reports that Chinese and U.S. officials are looking into the matter.
The US State Department expelled 17 Cuban diplomats from its Washington embassy past year after the incidents came to light.
"The department is taking this incident very seriously and is working to determine the cause and impact of the incident", said a U.S. embassy spokeswoman, Jinnie Lee.
The alert said a USA government employee in the southern Chinese city of Guangzhou reported "subtle and vague, but abnormal, sensations of sound and pressure".
The suspected "sonic attack" has been linked to "medically similar" episodes experienced by USA government staff in communist Cuba in late 2016.More news: Fognini fires up Italian Open crowd with win over Thiem
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"The US government is taking these reports seriously and has informed its official staff in China of this event", the statement added about the symptoms, which occurred from late past year to April.
The Chinese foreign ministry could not be immediately reached for comment.
The department also warned against attempting to locate the source of any unusual sounds.
The State Department's health advisory noted the cause of the symptoms is unknown.
During the investigation, the Cuban authorities did not find any "acoustic" or other weapons, which could be potentially damaging to the health of the U.S. diplomatic staff, even among those who resided very close to the building of the United States diplomatic mission.
Multiple workers in Havana complained of an incapacitating "high pitch beam of sound".
The People's Republic of China flag and the U.S. Stars and Stripes fly. "Instead, move to a location where the sounds are not present", the recommendation said.
Staff there reported symptoms including hearing loss, dizziness, fatigue and cognitive issues, though Cuban officials dismissed the idea of acoustic strikes as "science fiction" and accused Washington of slander.