China has announced new measures to stem the spread of the Delta variant of the coronavirus at a news conference in Beijing on Wednesday, focusing on strengthening epidemic controls at airports and borders.

The latest COVID-19 wave in China reportedly began with airport workers in Nanjing, who believably caught the virus while cleaning an inbound plane.

As of Wednesday, China had 144 medium- and high-risk areas - the most since the country adopted normalized COVID-19 prevention measures, said Mi Feng, a spokesperson of the National Health Commission. 

In response, authorities say frontline workers employed in international services at airports, land and water ports, including sailors, will be separated from their families during their work time.

"They'll work proper shifts and live in designated places to avoid contact with their families and community members," said Han Guangzu, vice chief of the Flight Standard Department of the Civil Aviation Administration of China.

Authorities say China will not issue exit and entry documents, including ordinary passports for citizens whose travel needs are "not necessary." But there are exceptions.

"For those applying for overseas study, employment, and business activities, their requests will be accepted, verified, and granted accordingly," said Liu Haitao, chief of the Frontier Inspection Department of the National Immigration Administration.

Liu said China will strengthen joint work with bordering countries to prevent imported cases from illegal immigrants. International mail, especially cold chain products, will be closely checked and handled in areas separate from domestic ones.