Why the Wuhan lab-leak theory is being taken seriously

Nearly a year and a half since Covid-19 was detected in the Chinese city of Wuhan, the question of how the virus first emerged remains a mystery.

But in recent weeks the controversial claim that the pandemic might have leaked from a Chinese laboratory - once dismissed by many as a fringe conspiracy theory - has been gaining traction.

Now, US President Joe Biden has announced an urgent investigation that will look into the theory as a possible origin of the disease.

So what do we know about the competing theories - and why does the debate matter?

It's a suspicion that the coronavirus may have escaped, accidentally or otherwise, from a laboratory in the central Chinese city of Wuhan where the virus was first recorded.

Its supporters point to the presence of a major biological research facility in the city. The Wuhan Institute of Virology (WIV) has been studying coronaviruses in bats for over a decade.

The laboratory is located just a few kilometres from the Huanan wet market where the first cluster of infections emerged in Wuhan.