The U.S. state department is urging staff in China to report any abnormal hearing or vision issues after an employee reported mystery symptoms while working at the U.S. consulate in the city of Guangzhou between late 2017 and April 2018.
Secretary of State Mike Pompeo said the incident was similar to suspected sonic attacks in Cuba.
The employee reported, "subtle and vague, but abnormal, sensations of sound and pressure".
"We are working to figure out what took place both in Havana, now in China as well," said Pompeo. "We have asked the Chinese for their assistance in doing that and they have committed to honouring the commitments under the Vienna Conventions to keep American Foreign Service officers safe"
In 2016 U.S. embassy staff in Cuba said they had suffered dizziness, nausea and hearing problems. The state department said 20 employees were affected and blamed Cuba. Havana denied any involvement and said the reports were political manipulation aimed at damaging bilateral relations.
China-US relations have been strained recently, amid fears of a trade war.