US chief medical advisor Anthony Fauci and many other scientists continue to believe the preponderance of evidence points toward a natural source for the coronavirus, National Public Radio reported on Friday.

"I'm more convinced than ever that this is a natural virus," said Robert Garry, a microbiologist at Tulane University who has analyzed the genome of the coronavirus.

That has been the case for every previous disease known to infect humans.

"The historical basis for pandemics evolving naturally from an animal reservoir is extremely strong," Fauci told senators at a hearing earlier last week. Ebola, HIV and the major influenza viruses all came from nature, he added.

The fact nobody has pinpointed the source for the new coronavirus is not particularly unusual, according to Garry. "It's just a matter of time before we find the progenitor in a bat or some other species," he said.

There is no evidence for human manipulation, said Ian Lipkin, a researcher at the Mailman School of Public Health at Columbia University.

In fact, the way the virus infects people is so quirky, he thinks it couldn't have been made in a lab.

"We would not have known how to design this virus, even if we had wanted to do so," he says. "When I say 'we', I really do mean the scientific community, whether we mean scientists in Europe or the US or China, for that matter."