US Secretary of State Mike Pompeo said that medical teams were en route to Guangzhou to investigate after an alleged sonic attack similar to those reported in Cuba.
In Cuba a year ago, 24 diplomats and their family members were left with mysterious injuries resembling brain trauma, which were suspected of being caused by a "sonic attack".
The government worker has returned to the U.S for further evaluation of the mild traumatic brain injury.
A health alert has been issued by the USA embassy in Guangzhou, warning Americans living or working in China to take action if "unusual sounds or piercing noises" are heard.
"We are working to figure out what took place both in Havana and now in China as well", Pompeo said.
The embassy, which issued a health alert to Americans living in China, said it could not link the case to health issues suffered by US government staff in Cuba dating back to late 2016. The worker was sent back to the United States for medical evaluation.
China's Foreign Ministry and National Health Commission did not immediately respond to faxed questions about the report.
The State Department said in its Wednesday statement that anyone who experienced "unusual acute auditory or sensory phenomena" while in China should move away from the source of the noise.
In an emailed notice to American citizens in China, the department said it wasn't now known what caused the symptoms in the city of Guangzhou, where an American consulate is located.
The US State Department has said that at least 24 individuals working at the US Embassy in Havana experienced health effects caused by these purported attacks. The Chinese government has assured the US that it is investigating the matter and taking appropriate measures, according to a State Department spokesperson.
Of the 21 medically confirmed U.S. victims, some have permanent hearing loss or concussions, while others suffered nausea, headaches and ear-ringing. Media reports have suggested that the Federal Bureau of Investigation has not been able to verify any evidence to support the sonic weapon theory. Pompeo said Wednesday he expects to have a report from the accountability review board investigating the incidents in Cuba by the middle of next week.
"The cause (of their symptoms) remains unknown but could be human-made", the Canadian government concluded.
Unlike their American counterparts, however, no Canadian envoy reported hearing any suspicious sound prior to falling ill.