Airports and airline companies in China will soon be required to carry out stricter epidemic prevention and control protocols, after the current COVID-19 outbreak was found to have spread from cabin cleaners, the industry regulator said on Tuesday.

The Civil Aviation Administration of China will soon issue its eighth guideline on epidemic prevention and control, Han Guangzu, deputy head of the administration's flight standards department, said in an online news conference on Tuesday.

Han said stricter "closed-circuit" measures for front-line airport and airline workers will be introduced, which could result in them spending time in quarantine and being kept from their families.

Front-line aviation workers will also be required to undergo more frequent nucleic acid testing, he said. Airline crews entering China will also be subjected to tighter isolation and health monitoring measures.

Civil aviation regulators at all levels will strengthen inspections to ensure airline companies and airports strictly follow the health guidelines, Han said.

Tougher protocols for suspension of international flights will also be introduced, he said. China currently handles about 230 international passenger flights a week, about 2 percent of the volume handled in 2019. There are about 3,700 international cargo flights every week, 2.5 times more than in 2019.

The administration will cooperate with other departments to evaluate the standards and effectiveness of quarantine measures for arriving aircraft. More medical guidance will also be provided to ground service workers, including cabin cleaners, aircraft maintenance workers and porters.

An outbreak started in Nanjing, Jiangsu province, after a group of cabin cleaners at Nanjing Lukou International Airport tested positive for COVID-19 on July 20. It was later found that they contracted the virus while cleaning an airplane.

An investigation found that the workers failed to obey sanitation and change-of-clothing protocols, which resulted in the virus being transmitted to other staff members.

A total of 327 confirmed cases in the province have been linked to the Nanjing airport, officials said at a news conference on the province's epidemic control work on Tuesday.

Han said two experts from the administration were sent to the airport to conduct an investigation. On July 22, the administration released a notice requiring all front-line workers to have nucleic acid tests as soon as possible.

On Saturday, the administration increased the frequency of the testing by ordering key front-line workers to have a nucleic acid test every two days.

Workers who have had direct contact with international passengers and cargo are required to be kept separate from those who work with domestic passengers and cargo. Both groups are not allowed to have contact with their family members or outsiders during work hours.