The US embassy in China issued a health alert yesterday 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.

US and Chinese authorities are investigating the matter after the employee, who was assigned to Guangzhou, was diagnosed with mild traumatic brain injury, said embassy spokeswoman Jinnie Lee.

In an alert e-mailed to US citizens in China, the embassy said it does not know what caused the symptoms or of any similar situations in the country.

In Cuba last year, the US disclosed that 24 diplomats and their family members had fallen victim to an unsolved mysterious attack that left them with injuries resembling brain trauma. Ten Canadian diplomats and their relatives also suffered a strange illness.

"We cannot at this time connect it with what happened in Havana but we are investigating all possibilities," a US official in Beijing said.

The embassy's health alert says the government employee "recently reported 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 message says.

"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. Instead, move to a location where the sounds are not present," it says, urging people with problems to see a doctor.

Lee said the employee experienced "a variety of physical symptoms" between late 2017 through April 2018. The person was sent to the United States and diagnosed with MTBI on May 18.

In Cuba, the American victims had associated the onset of their symptoms with "unusual sounds or auditory sensations," a State Department doctor said.

AGENCE FRANCE-PRESSE