The COVID-19 outbreak in Xi'an is the most serious in China since the lockdown of Wuhan, Hubei province, at the beginning of 2020, and the people of the whole country should give their strong support to the city in its efforts to fight it, a senior epidemiologist said.

Zeng Guang, former chief scientist of epidemiology at the Chinese Center for Disease Control and Prevention, said on Tuesday that the COVID-19 outbreak in Xi'an is caused by the Delta variant which spreads faster than the original coronavirus strain in Wuhan.

"The task is arduous, as the transmission chain has multiple links and moves in secret," said Zeng, a member of the National Health Commission's senior-level expert panel.

"In the face of such a serious threat, the whole country should fully support Xi'an in fighting against the pandemic," he told members of the media.

Zeng said he hoped Xi'an will find new ways of containing the spread of the coronavirus at the beginning of the outbreak.

"The COVID-19 spread in Xi'an today could also happen in other cities," he said.