Brussels: World leaders and organisations pledged $8 billion to research, manufacture and distribute a possible vaccine and treatment for COVID-19 on Monday, but the United States refused to contribute to the global effort.

Organisers included the European Union and non-EU countries Britain, Norway and Saudi Arabia. Leaders from Japan, Canada, South Africa and dozens of other countries joined the virtual event, while China, where the virus is believed to have originated, was only represented by its ambassador to the European Union.

Governments aim to continue raising funds for several weeks or months, building on efforts by the World Bank, the Bill and Melinda Gates Foundation and wealthy individuals, and turn the page on the fractious and haphazard initial response around the world.

"In the space of just few hours we have collectively pledged 7.4 billion euros ($8.1 billion) for vaccine, diagnostics and treatment against COVID-19,” head of the European Commission, Ursula von der Leyen, said after chairing the online event.

"This will help kick-start unprecedented global cooperation," she added.

It was however unclear what was new funding, as commitments made earlier this year may also be included, EU officials said.

Donors included pop singer Madonna, who pledged 1 million euros, von der Leyen said.

British Prime Minister Boris Johnson, who has recovered from a life-threatening battle with COVID-19, said the search for a vaccine was "the most urgent shared endeavour of our lifetime", calling for "an impregnable shield around all our people".

EU diplomats said the United States, which has the world's most confirmed COVID-19 cases, was not taking part.

A senior US administration official declined to say specify why the United States was not participating.

"We support this pledging effort by the EU. It is one of many pledging efforts that are going on and the United States is at the forefront," the official told reporters by telephone.

US President Donald Trump said last month that he would halt funding to the World Health Organisation, whose director general addressed the conference, over its handling of the pandemic.

The 8-billion-dollar goal was in line with expectations but is only an initial figure. Von der Leyen has said more money will be needed over time.