Just days earlier, Secretary of State Mike Pompeo announced Tuesday the formation of a task force in response to "unexplained health incidents" affecting USA diplomats and their family members.
The message urges staff and family members to contact their health care provider if they experience "any unusual, unexplained physical symptoms or events, auditory or sensory phenomena, or other health concerns".
The incidents have raised fears the unexplained issues that started in Cuba in 2016 have expanded.
Friday's alert called for people to look for symptoms including "dizziness, headaches, tinnitus, fatigue, cognitive issues, visual problems, ear complaints and hearing loss, and difficulty sleeping".
Mark Lenzi, a Foreign Service officer who was evacuated from Guangzhou this week along with his wife and 3-year-old son, described the noise as something like "marbles bouncing and hitting a floor, then rolling on an incline with a static sound". Now, reports the New York Times, American employees of the consulate in Guangzhou, in southern China, are reporting the same symptoms.
President Trump, Tillerson, and State Department officials have said they believe the Cuban government knows what occurred and who is responsible.
The United States State Department says a "number of individuals" were sent to the U.S. for further evaluation following initial screenings.
After several months of frustrating non-responses from Cuban officials, then-Secretary of State Rex Tillerson pulled almost all of the USA embassy staff out of Havana, a step that has soured relations between the Trump administration and the Cuban government.More news: Commerce Secretary: US reaches deal with China's ZTE
As soon as the department received medical confirmation that one USA government employee had suffered a "medical incident that was consistent with what American personnel in Havana, Cuba, had experienced", officials deployed a medical team to Guangzhou, China, to screen all US employees and family members who requested it, she said.
China on Thursday said it has investigated the U.S. allegations of mysterious sound attacks on its diplomats in the city of Guangzhou and found "no clue" even as two more American diplomats were evacuated after complaining of similar phenomena.
The Embassy Beijing and five US consulates in China, she said, held "townhall meetings" on May 23 "to allow employees to ask questions and raise concerns directly with senior leadership".
Canada in April also ordered families of diplomatic staff in Cuba to return home after mysterious health symptoms were detected in 10 Canadians stationed on the island.
Secretary of State Mike Pompeo released a statement on Tuesday saying the department established a task force last month "to direct a multi-agency response to the unexplained health incidents". Friday, it widened the alert to cover USA diplomatic staff in all of China.
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.
More than 2 million USA citizens travel to China each year, and about 175,000 Americans hold Chinese resident visas.
People working in The Canton Place complex, a few kilometers (miles) from the consulate, said Thursday they were just hearing about the incidents, reflecting a lack of coverage in China's entirely state-controlled media. "However I do not really feel that there is one thing to be very afraid of as a result of it is most likely a really particular case", Chen mentioned.