China's current COVID-19 prevention measures are still effective while the recent local outbreak in Nanjing, East China's Jiangsu province, may spread to more areas, a health official said on Saturday.

The latest COVID-19 surge with the Delta variant started in Nanjing July 20 after Nanjing Lukou International Airport's cabin cleaners tested positive for COVID-19 after cleaning an international flight.

The Delta variant of the COVID-19 virus can be transmitted faster and takes longer to be wiped out. Also, the recent virus cluster in Nanjing happened during the summer holiday season at a busy airport, which has led to the outbreak spreading to other cities and other parts of China, said He Qinghua, an official with the National Health Commission's Disease Prevention and Control Bureau.

"The risk of the outbreak spreading to more places in China still exists," He said at a news conference in Beijing on Saturday.

He added the current epidemic control measures are still effective to prevent the spread of the Delta variant of the COVID-19 virus.

Authorities in different areas must be better coordinated when tracking down high-risk cases. Also, the boundaries of high-risk areas must be drawn as fast as possible to cut the spread of the virus more effectively, He said.

Zhangjiajie, a popular tourist destination in Central China's Hunan province, has become the second worst-hit area after Nanjing during the latest outbreak. The first case in Zhangjiajie was related to the infections at Nanjing Lukou International Airport. The virus then soon started to spread among tourists, said Feng Zijian, a researcher at the Chinese Center for Disease Control and Prevention.

"People should avoid traveling to medium and high-risk areas. Meanwhile, those in medium and high-risk areas should cancel their travel plans," Feng said at the news conference.

Also, people who haven't received COVID-19 vaccinations are not advised to travel, Feng added.