A health warning to American citizens, sent via email, reads: "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". Should someone in China hear these noises, they should move somewhere where they don't hear them anymore, the alert says.
In an emailed notice to American citizens in China, the department said it was not now known what had caused the symptoms in the city of Guangzhou, where an American consulate is located.
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".
Secretary of State Mike Pompeo said the incident was similar to suspected sonic attacks in Cuba.
An investigation to establish the cause and impact has been launched by the US State Department. "The U.S. government is taking these reports seriously and has informed its official staff in China of this event".
But signaling the depth of their concern, the U.S. Embassy in Beijing and all five U.S. consulates in the country held town hall meetings Wednesday so employees could ask questions and raise concerns.
In an emailed notice to American citizens in China, the department said it was not now known what caused the symptoms in the city of Guangzhou, where an American consulate is located.
"Twenty-four people have had symptoms and findings consistent with what looks like a mild traumatic brain injury", State Department medical director Dr. Charles Rosenfarb told a Senate Foreign Relations subcommittee January 9 "The findings suggest that this is not an episode of mass hysteria". The state department said 20 employees were affected and blamed Cuba.
In 2016 USA embassy staff in Cuba said they had suffered dizziness, nausea and hearing problems.
It added the Chinese Government told the embassy it is also investigating and taking appropriate measures.
Responding to these claims, the Cuban Foreign Ministry denied any Cuban involvement in the alleged attacks.
The U.S.is determining whether or not this is a "sonic attack" and whether or not it's similar to what possibly happened in Cuba, a U.S. diplomatic official told CNN.
Cuban officials dismissed the idea of acoustic strikes as "science fiction" and accused Washington of slander.