The department said it wasn't aware of any similar situations in China, either within the diplomatic community or among others.
The U.S. a year ago chose to withdraw a large number of embassy staff from the country after diplomats stationed there complained of symptoms like hearing loss, dizziness, tinnitus, visual difficulties, headaches and fatigue.
A health alert sent Wednesday said a USA government employee assigned to the southern Chinese city of Guangzhou reported "subtle and vague, but abnormal, sensations of sound and pressure".
Embassy spokeswoman Jinnie Lee said the employee reported the symptoms beginning late past year and they lasted through April.
Wednesday's alert said the USA 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 US embassy in China issued a health alert Wednesday after a US government employee experienced an "abnormal" sound and suffered a mild brain injury - in an incident reminiscent of a mysterious illness that hit diplomats in Cuba.
The worker was sent to the United States for further evaluation.
The spokeswoman, Jinnie Lee, said the department is taking the incident "very seriously".
It added the Chinese Government told the embassy it is also investigating and taking appropriate measures.
The embassy warned workers in China to move away from the source of the noise if they experience "any unusual acute auditory or sensory phenomenon" with "unusual sounds of piercing noises".
Charles Rosenfarb, a doctor and director of the State Department bureau of medical services, said the symptoms were mixed but consistent with brain trauma. Symptoms included headaches and hearing loss. Media reports have suggested that the Federal Bureau of Investigation has not been able to verify any evidence to support the sonic weapon theory.
More than 20 members of staff in Havana were harmed in the "health attacks", according to the state department.
The US has held Cuba responsible, either for allowing the suspected attacks to happen or for carrying them out itself.
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The report, which first appeared in The Wall Street Journal , spurred lawmakers from both parties to accuse Mr. Treasury Secretary Steven Mnuchin on Monday emphasized the potential for China to buy liquefied natural gas.
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