US consulate staff in China have been told to beware of "unusual sounds" after an employee reported mystery hearing and vision symptoms.
In a statement, the employee was said to have experienced "subtle and vague, but abnormal, sensations of sound and pressure", which officials are saying could be indicative of a sonic attack.
Secretary of State Mike Pompeo said the incident was "medically similar" to a recent suspected sonic attacks on diplomatic staff in Cuba.
He added that medical teams were on their way to Guangzhou, where the US embassy is located, to investigate.
"We are working to figure out what took place, both in Havana and in now in China as well," Pompeo said.
"We've asked the Chinese for their assistance in doing that and they have committed to honouring their commitments under the Vienna convention to keep American foreign service officers safe."
According to the BBC, the US state department said it was taking the incident "very seriously", but had not accused China of being behind it, despite tensions between the two countries being high at the moment.
"We do not currently know what caused the reported symptoms and we are not aware of any similar situations in China, either inside or outside of the diplomatic community," the US diplomatic statement said.
"The US government is taking these reports seriously and has informed its official staff in China of this event."
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. Instead, move to a location where the sounds are not present."
An embassy spokeswoman said the Chinese government had given assurances that it was also investigating and taking appropriate measures.
Cotton seedling freezes to death as Chang'e-4 shuts down for the Moon's 14-day lunar night
Fortnite easily out-earns PUBG, Assassin's Creed Odyssey and Red Dead Redemption 2 in 2018
Meteor showers as a service will be visible for about 100 kilometres in all directions
Saturn's rings only formed in the past 100 million years, suggests analysis of Cassini space probe data
New findings contradict conventional belief that Saturn's rings were formed along with the planet about 4.5 billion years ago