China's top disease control official has said the country is formally considering mixing COVID-19 vaccines, as a way of further boosting vaccine efficacy.

Available data shows Chinese vaccines lag behind others including Pfizer and Moderna in terms of efficacy, but require less stringent temperature controls during storage.

The currently available vaccines "don't have very high rates of protection", Gao Fu, the director of the Chinese Centers for Disease Control and Prevention, told a conference in the Chinese city of Chengdu on Saturday.