However, Dutch virologist and World Health Organization team member Marion Koopmans said that species more susceptible to the virus - including bamboo rats, badgers and rabbits - were sold at Wuhan's Huanan market, the site of an early virus cluster, and could be an entry point for trace-back investigations.

While the figures reported by countries to the World Health Organization for the week ending February 8 are still incomplete, the global body said so far about 1.9 million newly confirmed cases were registered worldwide, down from more than 3.2 million the previous week.

In addition to sampling more wild animal reservoirs - especially bats - in and outside China, Ben Embarek suggested re-testing samples using "new approaches" to blood tests and looking for more early cases that went undetected in Wuhan in December 2019.

China, meanwhile, is keen that the next stage of the virus origin investigation takes place in another country.

Tedros, the WHO's director-general, said that the Geneva-based body had this week held its first meeting to help define and diagnose what he called post-COVID condition, also known as long COVID.

Experts believe the virus is likely to have originated in animals before spreading to humans, but they are not sure how.

Chinese scientists and the WHO's team of global researchers said this week that the coronavirus most likely first appeared in humans after jumping from an animal, and an alternate theory that the virus leaked from a Chinese lab was unlikely.

But he also said they are still far from identifying the origins of the coronavirus.

Ghebreyesus said this at a briefing on Friday monitored by our correspondent.

The team called for further investigation into the possibility of "cold chain" transmission, referring to the transport and trade of frozen food.

The group's leader, Peter Ben Embarek, added that it was "extremely unlikely" that the virus came from a lab in Wuhan.

"We've done a lot of work in China and if you map that back it starts to point towards the border and we know that there is very little surveillance on the other side in the whole region of South East Asia", he told the BBC's John Sudworth in Wuhan.

This spike in mortality comes as Africa's second wave of cases which began in October 2020 seems to have peaked on 6 January 2021.

China has strongly denied this, and says the Wuhan Institute of Virology was not studying related viruses.

In April, US state department cables came to light suggesting that embassy officials were anxious about biosecurity there. We have always said that this mission would not find all the answers, but it has added important information that takes us closer to understanding the origins of the virus.

He said the laboratory theory was "not in the hypotheses that we will suggest for future studies".