The cases in Guangzhou — and now possibly Shanghai and Beijing — are similar to a wave of illnesses that struck Americans working at the embassy in Havana, Cuba, beginning in fall 2016. Another American there was reported last week to have symptoms, bringing the total number of those afflicted by what have been described as “sonic attacks” to 25.

It remains unclear whether the cases in Shanghai and Beijing — which have not been previously reported — were related to what officials described as “subtle and vague, but abnormal, sensations of sound and pressure” experienced at an apartment tower in Guangzhou where a number of consulate employees live.

The sounds and sensations in Cuba, and now China, have been variously attributed to sophisticated electronic eavesdropping efforts or a form of aural harassment, with some pointing fingers at Russia or China. Other experts have raised the possibility of environmental factors or even mass hysteria.

American officials in China declined to comment or did not respond to inquiries. But in a written response on Saturday, the State Department said that “several staff and family members” had been sent to the United States for further evaluation. The statement suggested that some might have been evacuated for “other unrelated issues.”

The statement said that only one of those evacuated so far had been diagnosed with mild traumatic brain injury: the first employee who was evacuated in April after complaining of health issues caused by the sounds and sensations.