The US State Department has evacuated more staff from China over fears they may have been hit by a mysterious illness that has struck other colleagues in the Asian country and Cuba.

The department said Wednesday that "a number of individuals" were sent to the United States for further evaluation following initial screenings.

A medical team was sent to the southern city of Guangzhou after an American employee who had experienced strange sounds was diagnosed with a brain trauma last month, reviving fears that a 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 government employees and family members who requested it, the State Department said.

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.