The alert, the second in just two weeks, urged Americans to seek medical help in the event they suffered any "unusual, unexplained physical symptoms or events, auditory or sensory phenomena, or other health concerns".
The unexplained health problems have already prompted the evacuation of a number of U.S. government employees from the southern city of Guangzhou, where a USA consulate is based.
At least one government worker in Guangzhou began complaining last month of symptoms similar to the mysterious condition that plagued 24 Havana-based diplomats and their families beginning in 2016, according to state officials.
The case revived fears that a United States rival has developed some kind of acoustic or microwave device after similar symptoms were reported among American diplomats and their families in Cuba in 2016.
Earlier, the United States embassy in China issued a health alert today after a U.S. government employee experienced an "abnormal" sound and suffered a mild brain injury - in an incident reminiscent of a mysterious illness that hit diplomats in Cuba.
Officials said "a number of individuals" returned to the USA for "further evaluation and a comprehensive assessment of their symptoms and findings". The diplomats who reported problems with hearing loss, balance, vision, sleep, and headaches in Cuba were living in hotels and other dense dwellings-places where a listening device or other unknown technology could have easily been planted nearby. Instead, it said, they should move to a different location.
US doctors later diagnosed that first employee, who the State Department evacuated from the Guangzhou-based consulate in April, with brain trauma.
US investigators initially said the illnesses in Cuba could have been the result of a "sonic attack".
Requested in regards to the newest incidents, Chinese language Overseas Ministry spokeswoman Hua Chunying mentioned the US had not formally raised the matter with Beijing.
"As for the latest incident, my understanding is that the United States side hasn't had any formal communication with the Chinese side about it", foreign ministry spokeswoman Hua Chunying said Thursday at a regular press briefing.
"At present, there's been no discovery of clues or the reason causing the situation the United States mentioned", Hua told a regular news briefing in Beijing, adding that China protected diplomats according to worldwide convention.
The US is bringing back a group of diplomats from China for further medical evaluation over concerns they were suffering from a mysterious illness similar to those reported by its personnel in Cuba, an official said today. In 2016, 24 people - all embassy workers and their families there - suffered the same symptoms at the USA embassy in Havana, Cuba.
The symptoms were similar to those found in the case of USA diplomatic personnel who worked in Cuba, including mild traumatic brain injury.
The Penn team said the patients from Cuba experienced persistent disability though rehabilitation therapy customized for them seemed to help.
In April, Canada also ordered families of diplomatic staff in Cuba to return home after mysterious health symptoms were detected in 10 Canadians stationed on the island. Friday, it widened the alert to cover US diplomatic staff in all of China.
Four American members of staff at the USA consulate in Guangzhou referred Reuters to the Beijing embassy press office when asked about the situation.
It serves four southern provinces with a combined population of more than 204 million and processes more than 1 million visa applications of all types annually. It is also the only US diplomatic installation in China authorized to process immigrant visas and handle adoptions.