The State Department sent a medical team to Guangzhou, China, recently after a government employee reported experiencing abnormal sound and pressure.
President Donald Trump has said he believed Cuba knew about the attacks and could have stopped them. "We are in contact with USA officials and are closely monitoring developments".
In testimony before the Senate Foreign Relations Committee last month, U.S. Secretary of State Mike Pompeo said China had "said all the right things and have demonstrated their willingness to help us identify the vector which led to this medical incident".
One official said that "a sizable number" of people working in Guangzhou had requested examinations, which are being carried out in the consulate's medical facilities.
Cuba has denied targeting embassy staff, and the United States has not blamed the country's government for the suspected attacks.
A USA medical team was screening more Americans who work in a southern Chinese city as the State Department confirmed evacuating a number of government workers who experienced unexplained health issues like those that have hurt US personnel in Cuba and China.
The team arrived earlier this week, and Nauert said the medical screenings were ongoing.
These follow an earlier evacuation of a US government employee in April who reported experiencing "subtle and vague, but abnormal, sensations of sound and pressure", according to the State Department.
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Four American members of staff at the USA consulate in Guangzhou referred Reuters to the Beijing embassy press office when asked about the situation.
Lenzi also said the employee evacuated last month was his next-door neighbor, a fellow Foreign Service officer who was diagnosed with mild traumatic brain injury.
The latest round of evacuations, which began Wednesday in China, was the first sign that the unexplained ailments have now broadened and threaten to become a full-blown health crisis like the one that affected at least 24 diplomats and their families in Cuba.
A state department release on Tuesday made no reference to the possibility of a deliberate attack in China.
Secretary of State Mike Pompeo said at a congressional hearing in May that the symptoms experienced by a U.S. diplomat a year ago in Guangzhou "are very similar and entirely consistent with the medical indications that have taken place to Americans working in Cuba".
Last year, 24 United States diplomats and their family members in Cuba fell victim to mysterious "attacks" that left them with injuries resembling brain trauma.