China will focus first on vaccinating high-risk groups over the winter and spring before widening the inoculation to the general public, a senior health official said on Saturday.

Zeng Yixin, vice minister of China's National Health Commission (NHC) and director of State Council's vaccine R&D working group, warned that China's COVID-19 prevention efforts were under increasing pressure as temperatures fall.

"During the winter and spring seasons, carrying out novel coronavirus vaccination work among some key population groups is of great significance to epidemic prevention," he told a briefing.

China aims to actively build group immunity, and the vaccination of high-risk groups - which include workers in the cold chain industry, customs, healthcare, markets and public transport - is just the first part of a "step-by-step programme", he added.

China has included two candidate vaccines from Sinopharm and one from Sinovac Biotech Ltd in an emergency-use programme launched in July, targeting specific high-infection risk groups such as medical workers and border inspectors.

It has also approved a vaccine from CanSino Biologics Inc for military use but has not approved any vaccine for use among the general public.

Zheng Zhongwei, the NHC official heading China's COVID-19 vaccine development team, said China had administered more than 1 million emergency doses to members of high-risk groups since July and "no serious adverse reactions" have been detected so far.

"For the vaccines where we are moving quite fast, the number of cases required for the interim stage of Phase III clinical trials have already been obtained," Zheng said, though he didn't specify which products.

Data has been submitted to the medical products regulator, which will approve the vaccines if they meet the necessary conditions, he added.