Last month, the US State Department urged its staff in China to alert them to any abnormal hearing or vision issues after an employee reported mystery symptoms.
The U.S. government has deemed the Cuba incidents "specific attacks" on American workers but hasn't publicly identified a cause or culprit.
China earlier said it had looked into the case announced last month but came up with no clues about the cause of the symptoms.
The State Department has sent a medical team to China to offer medical screenings to all American government workers and family members who want them.
China reaffirmed today that its official investigations had not found any evidence of alleged health problems of US diplomats working in this country.
"If the U.S. makes formal contact with us, China will continue necessary investigations in an earnest and responsible manner and maintain close communication and cooperation with the U.S.", Hua said at a regularly scheduled news conference.
Symptoms suffered by the diplomats have included hearing loss, tinnitus, vertigo, headaches and fatigue, a pattern consistent with "mild traumatic brain injury", State Department officials have said.More news: Kevin Love Wants to Finish His Career With LeBron James on Cavs
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State Department spokeswoman Heather Nauert also said at the time that the Chinese government assured the State Department that it is investigating the symptoms felt by the USA government employee.
Security guards outside the Guangzhou consulate on Thursday told reporters to leave the area and not attempt to talk to consulate staff.
In May, U.S. Secretary of State Mike Pompeo said the symptoms experienced by the American worker evacuated from China in April were the same as those exhibited by diplomats in Cuba during testimony before the House Foreign Affairs Committee.
In 2017 in Cuba at least 22 American diplomat and their family members have suffered as a result of the mysterious "acoustic attack".
The incidents have raised concerns that a government or agency may be targeting the USA with a new type of sonic weapon. There are about 170 USA diplomats or employees and their families in Guangzhou.
Since the incident, other employees from the consulate and their families have been evacuated. According to the statement, authorities could not find the source of the sound.