Dozens of American diplomats complained of suffering from illnesses following mysterious sonic attacks.
"[An embassy staffer] has suffered a medical incident consistent with what other U.S. government personnel experienced in Havana, Cuba," the State Department said.
An employee at the U.S. Consulate in Guangzhou and his family left China on Wednesday after hearing strange noises and experiencing excruciating headaches.
From Bruce Springsteen records to pirate-repelling acoustic devices, sonic weapons have a long military history. But they have very different effects than those reported in China and Cuba.
"A U.S. government employee in China recently reported subtle and vague, but abnormal, sensations of sound and pressure," the official warning said.
A warning noted that the victims suffered ear complaints, hearing loss and dizziness.
Scientists may have figured out the mysterious symptoms.