A chartered plane carrying 163 Chinese citizens from Iran landed in Lanzhou, the capital city of Northwest China's Gansu province, on Thursday afternoon, bringing the total number of Chinese returned from Iran to 309 as the COVID-19 epidemic develops further.

On Wednesday afternoon, China Southern Airlines Flight CZ3002 arrived in Lanzhou, carrying the first group of 146 Chinese passengers from Iran.

All returned passengers, 309 in total, are now under quarantine in the city's Lanzhou New Area after their temperatures were checked.

Foreign Ministry spokesman Zhao Lijian said on Wednesday the ministry is closely following developments overseas and will take necessary measures to help bring Chinese citizens back if the epidemic develops further and poses a serious threat.

As of Tuesday, Chinese customs had found 6,728 inbound passengers who showed symptoms of possible novel coronavirus infection, and 75 were later confirmed to be infected, the General Administration of Customs said on Wednesday.