The State Department said the employee, stationed in Guangzhou, shows symptoms of a mild traumatic brain injury.
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.
"The embassy learned that the clinical findings of this evaluation matched mild traumatic brain injury", Lee said.
"We can not at this time connect it with what happened in Havana but we are investigating all possibilities", a USA embassy official in Beijing told AFP on the condition of anonymity.
Previous year in Cuba, the United States reported that some of its personnel and family members experience a range of symptoms, often after hearing an unusual sound, but the cause is still unknown.
The State Department has urged USA citizens in China to report any "symptoms or medical problems" they notice while in the country to a medical professional after a government employee experienced "subtle and vague, but abnormal, sensations of sound and pressure".
"The US government is taking these reports seriously and has informed its official staff in China of this event". The person was sent to the United States and diagnosed with MTBI on May 18.
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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".
A spokesperson at the U.S. Embassy in Beijing confirmed to CBS News that from late 2017 through April 2018, a U.S. government employee assigned to the Guangzhou Consulate reported "a variety of physical symptoms".
"The (State) Department is taking this incident very seriously and is working to determine the cause and impact of the incident", Lee said.
The diplomats said when they left rooms in the embassy, the symptoms and sounds immediately stopped.
"We can not at this time connect it with what happened in Havana but we are investigating all possibilities", a USA embassy official in Beijing told AFP news agency on condition of anonymity.
The still-unexplained incidents sparked a rift in US-Cuban relations, while investigators have chased theories including a sonic attack, electromagnetic weapon or flawed spying device. Symptoms included headaches and hearing loss.
The cause of those incidents remains unresolved.