The biggest challenge in combating the novel coronavirus outbreak right now is complacency as confirmed cases decline, a World Health Organization expert said on Monday.

"A huge part of the world, including China, is still susceptible to the novel coronavirus," said Canadian epidemiologist Bruce Aylward, head of the WHO mission team, at a news conference of the WHO-China Joint Mission on COVID-19 in Beijing. "It's a new virus, so people do not have immunity to it." he added.

"When people are used to dealing with a virus, they tend to get complacent. And that is always the single biggest risk," he said.