BEIJING — China said Thursday that it is prepared to help get to the bottom of a mysterious illness that has sickened Americans working at the US Consulate in the southern part of the country and led to the evacuation of a number of diplomats this week.

The Chinese Foreign Ministry said that the government had already carried out an investigation in May after the first case of an American diplomat becoming sick in the city of Guangzhou was reported in April.

At the time, Chinese investigators had not been able to determine the source of the diplomat’s illness, the ministry said.

US diplomats at the consulate have complained of symptoms similar to those “following concussion or minor traumatic brain injury,’’ and may have been targets of attacks involving strange sounds, the State Department said Wednesday.

The symptoms — and the apparent causes — are similar to those that affected 24 US personnel in Cuba in 2016.

The State Department has not said how many of the more than 100 US employees at the consulate in Guangzhou have been evacuated so far. The ill diplomats complained of unusual sounds in their apartments, which are not far from the consulate.

Those evacuated were being taken for testing to the University of Pennsylvania Center for Brain Injury and Repair, where a team of researchers had examined the cases from Cuba.

China had not been informed by the United States of the latest evacuations, a ministry spokeswoman, Hua Chunying, said Thursday.

“If the US comes to us regarding this case again, we will investigate it seriously and keep close cooperation with the US,’’ Hua said.

She added that China took seriously its obligations under the Vienna Convention, an international accord that requires governments to protect the diplomats of other countries.

The illnesses have the potential to further upset relations between China and the United States, already strained over trade disputes and North Korea.

Last year, the State Department pulled from Cuba a large number of diplomats who had developed vertigo, sleeplessness and cognitive impairment, saying the country was unable to protect them.

US officials have raised questions about whether Russia, or China, might be involved separately or in tandem in targeting the diplomats.

In an article in The Journal of the American Medical Association, brain researchers at the University of Pennsylvania described the sickness as a new neurological syndrome.

The odd nature of the illness could put the Chinese in a difficult predicament, even if they want to be diligent about trying to protect US and other foreign officials, diplomatic experts said.

The United States would no doubt press China to uncover the cause of the illnesses and to stop it, but it could prove difficult, or too embarrassing, for China to do so, the experts said.