The head of the World Health Organisation has said the world is in "a very dangerous period" of the Covid-19 pandemic, noting that the more contagious Delta variant has been identified in nearly 100 countries.

At a press briefing, Tedros Adhanom Ghebreyesus said the Delta variant, first found in India, is continuing to evolve and mutate, and it is becoming the predominant Covid-19 virus in many countries.

"I have already urged leaders across the world to ensure that by this time next year, 70% of all people in every country are vaccinated," he said, adding that would effectively end the acute phase of the pandemic.

He noted that three billion doses of vaccine have already been distributed and "it's within the collective power of a few countries to step up and ensure that vaccines are shared".

Of the vaccine doses given globally, fewer than 2% have been in poorer countries.

Although rich countries including Britain, the US, France and Canada have pledged to donate one billion Covid-19 vaccines, the WHO estimates 11 billion doses are needed to immunise the world.

Meanwhile the WHO is advising the International Olympic Committee in the run-up to the Games in Tokyo and has urged caution in order to track the spread of the coronavirus, a senior WHO official said on Friday.

"The IOC and others have outlined their plans in taking their approach for the Olympics, and we have been engaging with them and advising them on the best use of those plans," the WHO's technical lead on COVID-19, Maria van Kerkhove, told a news conference.

She said the WHO was learning from the Euro 2020 soccer tournament, adding: "If the virus is present and precautions are not in place the virus will spread."