World Health Organisation member states agreed on Tuesday to an independent probe into the UN agency's coronavirus response as US criticism mounted over its handling of the pandemic.

Countries taking part in the WHO's annual assembly, being held virtually for the first time, adopted a resolution by consensus urging a joint response to the crisis.

The resolution, tabled by the European Union, called for an "impartial, independent and comprehensive evaluation" of the international response to the pandemic, which has so far infected more than 4.8 million people and killed over 318,000.

It said the investigation should include a probe of "the actions of WHO and their time-lines pertaining to the COVID-19 pandemic".

The US did not disassociate itself from the consensus as some had feared after Washington chastised the WHO on the first day of the assembly Monday and lashed out further against China over its role in the outbreak.

Tuesday's resolution at the WHO assembly -- which is not binding and mentioned no countries by name -- also called for nations to commit to ensuring "transparent, equitable and timely access" to any treatments or vaccines developed against COVID-19.

And it addressed the controversial issue of the origin of the virus, which first emerged in China late last year, urging the WHO to help investigate "the zoonotic source of the virus and the route of introduction to the human population".