The team of WHO-led independent experts trying to determine the origins of the new coronavirus arrived on January 14 in Wuhan where they are holding teleconferences with Chinese counterparts during a two-week quarantine before starting work on the ground.

The US, which has accused China of hiding the extent of its initial outbreak, has called for a "transparent" WHO-led investigation and criticised the terms of the visit, under which Chinese experts have done the first phase of research.

Garrett Grigsby of the Department of Health and Human Services, who heads the US delegation, said China should share all scientific studies into animal, human and environmental samples taken from a market in Wuhan where the SARS-CoV-2 virus is believed to have emerged in late 2019.

Comparative analysis of such genetic data would help to "look for overlap and potential sources" of the outbreak that sparked the COVID-19 pandemic, he told the WHO's Executive Board.

"We have a solemn duty to ensure that this critical investigation is credible and is conducted objectively and transparently," said Grigsby, who also referred to virus variants found in the UK, South Africa and Brazil.

Sun Yang, director-general of the health emergency response office of China's National Health Commission, told the board: "The virus origin studies are of a scientific nature. It needs coordination, cooperation. We must stop any political pressure."

Australia's delegation also called for the WHO team to have access to "relevant data, information and key locations".

"There are no guarantees of answers," WHO emergency chief Mike Ryan told reporters last Friday.

"It is a difficult task to fully establish the origins and sometimes it can take two or three or four attempts to be able to do that in different settings."

Australian Associated Press