Donald Trump has been accused of engaging in conspiracy theories over "unhelpful" claims that the coronavirus outbreak could have originated in a Chinese laboratory.
The US President said he had seen evidence that the virus came from an infectious diseases laboratory in Wuhan and suggested its release was a "mistake".
But Dr Michael Head, a senior research fellow in global health at the University of Southampton, said: "We have good evidence from the genomics research that the virus is not man-made. The scientific world has moved on from this idea.
"It is unhelpful for high-profile individuals to repeat the debunked conspiracy theories because it undermines the public health response."
Brendan Wren, professor of medical microbiology at the London School of Hygiene and Tropical Medicine, also voiced caution.
"Having been to Wuhan a number of times and having had infectious disease researchers from Wuhan working in my labs in London, I don't believe that there have been any deliberate or nefarious activities with the SARS-Cov-2 virus," he said.
He added that the city of Wuhan has "excellent state-of-the-art infectious disease facilities".
"It is generally accepted that the virus has mutated naturally and it has been very difficult to contain within the human community," professor Wren said.
"It should be noted that pandemics occur throughout history. We have them every year.
"These include other viruses and bacteria - for example, antibiotic-resistant bacteria. We know (that they), through human activities such as travel, spread rapidly worldwide.
"Pandemics happen naturally and it is unnecessary to invoke a conspiracy theory."
Conservative MP Tom Tugendhat, chairman of the House of Commons Foreign Affairs Committee, said the Mr Trump's comments came "as no surprise".
Professor David Harper, former chief scientist and director-general for public health at the UK's Department of Health, said theories around the virus's origin had been circulating since January.
He added: "I think it's one of those situations where there is plenty of room for speculation and there are probably, undoubtedly, different agendas at play."
But Prof Harper, now a consultant for the Chatham House think tank, admitted: "The weight of scientific opinion seems to be fairly and squarely on the side of this being a naturally occurring disease."
Mr Trump's intelligence agencies are examining the suggestion from the US President and his aides that Covid-19 could have been unleashed accidentally from China.
On Thursday the Office of the Director of National Intelligence issued a statement from the intelligence community saying that it "concurs with the wide scientific consensus that the Covid-19 virus was not man-made or genetically modified".
It added: "The (intelligence community) will continue to rigorously examine emerging information and intelligence to determine whether the outbreak began through contact with infected animals or if it was the result of an accident at a laboratory in Wuhan."
Speaking on Thursday, Mr Trump said: "It's a terrible thing that happened.
"Whether they made a mistake or whether it started off as a mistake and then they made another one, or did somebody do something on purpose?
"Certainly it could have been stopped. They either couldn't do it from a competence standpoint or they let it spread. It got loose, let's say, and they could have capped it."
The Chinese government said any claims that the coronavirus was released from a laboratory were "unfounded and purely fabricated out of nothing".