The department said Wednesday that "a number of individuals" were sent to the United States for further evaluation following initial medical screenings.
A medical team was sent to the southern city of Guangzhou after an American employee who had experienced strange sounds was diagnosed with brain trauma last month, reviving fears that US rival has developed some kind of acoustic or microwave device.
US officials have said that the employee's symptoms were consistent with the ailments that US diplomats experienced in Cuba last year.
After the first incident in Guangzhou, medical tests were offered to US
"The medical screenings are ongoing for any personnel who have noted concerning symptoms or wanted baseline screening," State Department spokeswoman Heather Nauert said in a statement.
"US medical professionals will continue to conduct full evaluations to determine the cause of the reported symptoms and whether the findings are consistent with those noted in previously affected government personnel or possibly completely unrelated."
Last year, 24 US diplomats and their family members in Cuba fell victim to mysterious "attacks" that left them with injuries resembling brain trauma. Ten Canadian diplomats and their relatives also suffered a strange illness.
Washington has said in the past that Cuban authorities must take responsibility for the safety of US diplomats on their soil, but the Havana government denies any knowledge of an attack.
The US has set up a task force to oversee the response to the mystery ailments among diplomats in China and Cuba, Secretary of State Mike Pompeo said Tuesday.
The State Department has warned that US diplomats should alert their mission's medical staff "if they note new onset of symptoms that may have begun in association with experiencing unidentified auditory sensations."
"Reported symptoms have included dizziness, headaches, tinnitus, fatigue, cognitive issues, visual problems, ear complaints and hearing loss, and difficulty sleeping," the statement said.
The cases come at a sensitive time in relations between the United States and China, with the two nations mired in negotiations aimed at prevening a trade war and exchanging heated rhetoric over Beijing's claims to the South China Sea.
The Chinese foreign ministry said Thursday that its investigation into the first case has not yielded any clues as to the cause of the incident.
"As for the latest incident, my understanding is that the US side hasn't had any formal communication with the Chinese side about it," foreign ministry spokeswoman Hua Chunying said at a regular press briefing.
Hua said Beijing learned about the latest cases through a report in The New York Times
...which still proudly displays Walter Duranty's Pulitzer prize...
"I think that if there is any problem, the US can communicate with the Chinese side, and China will continue to adopt a responsible attitude and conduct a serious investigation," she said.