GENÈVA, Switzerland (AFP) — The international investigation into the COVID-19 pandemic's origins in China will publish its report in the week of March 15, the World Health Organization's chief has said.

The report was originally due to be published in two stages: an initial summary in February followed by the full text. However, they will both now be released at the same time, said WHO director-general Tedros Adhanom Ghebreyesus.

"I know that many member states are eager to see the report of the joint WHO-led study on the origins of the SARS-CoV-2 virus — and of course so am I," Tedros said in a speech to the UN health agency's member countries on Thursday.

"The team is working on its final report as well as an accompanying summary report, which we understand will be issued simultaneously in the week of the 15th of March.

"Rest assured that when the reports are ready, we will ask the expert team to share the reports with member states ahead of their release, and to brief you on the findings."

The first COVID-19 cases were reported in the Chinese city of Wuhan in December 2019.

The international investigation in the city only began in January 2021 and wrapped up last month.

A team of international scientific experts spent four weeks in Wuhan visiting sites linked to early cases.

Experts believe the disease originated in bats and could have been transmitted to humans via another mammal.

Although the mission to Wuhan failed to identify the source of the virus, the experts were dismissive of the theory that it leaked from a virology laboratory in the city at a press conference before leaving China.

However, when the team leadership returned to Geneva, Tedros said that, "all hypotheses remain open".