G20 nations emphasised the need for global access to coronavirus vaccines at a Saudi-hosted virtual summit dominated by efforts to tackle the pandemic and the worst global recession in decades.

World leaders, including US President Donald Trump who is refusing to concede a bitter election, popped up in multiple windows across a flickering screen, in a high-stakes webinar held amid the raging pandemic.

The leaders are huddling online for the two-day gathering as international efforts intensify for a large-scale rollout of coronavirus vaccines after a breakthrough in trials, and as calls grow for G20 nations to plug a €4.5 billion funding shortfall.

"Although we are optimistic about the progress made in developing vaccines, therapeutics and diagnostics tools for Covid-19, we must work to create the conditions for affordable and equitable access to these tools for all people," said Saudi King Salman, the summit's host.

"We have a duty to rise to the challenge together during this summit and give a strong message of hope and reassurance to our people by adopting policies to mitigate this crisis," he told world leaders in opening remarks.

Chinese President Xi Jinping spoke of the need to build a "global firewall against Covid-19" as he called on G20 nations to help distribute vaccines "fairly and efficiently", according to state news agency Xinhua.

And French President Emmanuel Macron said the health crisis was "a test for the G20", stressing there "will be no effective response to the pandemic unless it is a global response".

As the trailblazing event got under way, there had been some early quirks, with someone heard telling King Salman that "the whole world is watching" before the event started and Mr Xi apparently having to call for technical help.

With Saudi hopes for a grand coming-out parade dashed due to the pandemic, the event has been reduced to brief online sessions of what observers call "digital diplomacy".

Despite having to abandon much of the usual summit pageantry, Saudi Arabia launched the meeting with an aerial acrobatics display over Riyadh.

Along with Mr Xi and Mr Macron, Turkish President Recep Tayyip Erdogan also addressed the summit, where sources said climate change was among the issues topping the agenda.

Mr Trumpwas briefly dialled into the meeting and "spoke about the aggressive actions and safety measures the United States took to protect the vulnerable, pioneer groundbreaking treatments, and develop vaccines and therapies at record-setting speed, which will save millions of lives," according to a White House statement. He then went golfing.

Many G20 leaders have already congratulated his rival, President-elect Joe Biden.

G20 nations have contributed more than €17.7bn to combat the pandemic, which has infected 56 million people globally and left 1.3 million dead, and injected €9.2 trillion to "safeguard" the virus-battered world economy, organisers said.

But the group's leaders face mounting pressure to help stave off possible credit defaults across developing nations.

Last week, its finance ministers declared a "common framework" for an extended debt restructuring plan for virus-ravaged countries, but campaigners say the measure is insufficient.

The ministers had extended a debt suspension initiative for developing countries until June next year but UN Secretary-General Antonio Guterres has pushed for a commitment to push it until the end of 2021.

International Monetary Fund managing director Kristalina Georgieva has warned that the global economy faces a hard road back from the Covid-19 recession, even as vaccines are now in sight.

G20 nations must help plug the €3.8bn funding gap in the so-called ACT-Accelerator, Norway's prime minister, South Africa's president and the heads of the European Union and the World Health Organization demanded in a joint letter to the group.

The programme promotes an equitable distribution of Covid-19 vaccines including poor countries to rein in the pandemic.