Saudi Arabia opened the G20 summit in a first for an Arab nation, with the virtual forum dominated by efforts to tackle the coronavirus pandemic and the worst global recession in decades.

The two-day meeting of the world's wealthiest nations comes as President Donald Trump refuses to concede a bitter election and campaigners criticise what they call the G20's inadequate response to the crippling economic crisis.

World leaders are huddling virtually 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 €4.3bn funding shortfall.

Amid a raging pandemic, the summit is reduced to brief online sessions of "digital diplomacy", and Saudi hopes for a grand coming-out parade have been dashed.

"It is unfortunate that we are unable to host you in person in Riyadh, due to the exceptional circumstances that we are all facing this year," King Salman, the summit's hosts, told world leaders in opening remarks via video conference.

"Our peoples and economies are still suffering from this shock. However, we will do our best to overcome this crisis through international cooperation," he said, as de facto leader Crown Prince Mohammed bin Salman looked on.

Despite having to abandon much of the usual summit pageantry, the kingdom launched the event with an aerial display of passenger and aerobatic planes over Riyadh.

And denied the opportunity to take the traditional "family photo", a montage of G20 leaders was projected onto the ruins of the historical town of Diriyah during a gala event last night.

German Chancellor Angela Merkel, Chinese President Xi Jinping and Russian leader Vladimir Putin are among leaders expected to speak at the summit, with climate change among the issues topping the agenda, sources close to the organisers said.

Mr Trump is also taking part but it is unclear whether the US President, who continues to reject his election loss, will make an address.

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

As the trailblazing event got under way, there were some early quirks, with someone telling King Salman that "the whole world is watching" before the event started, Mr Xi apparently having to call for technical help, and French President Emmanuel Macron chatting to an aide off camera.

'Bolder measures'

G20 nations have contributed more than €20 billion to combat the pandemic, which has infected 56 million people globally and left 1.3 million dead, and injected €10 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 extend the initiative 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 downturn even as vaccines are now in sight.

G20 nations must help plug a $4.3bn funding gap in the so-called ACT-Accelerator, demanded a joint letter to the group from Norway's prime minister, South Africa's president, the heads of the European Union and the World Health Organization.

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

'Serious abuses'

Saudi Arabia's human rights record has cast a shadow on the gathering, as campaigners and families of jailed activists launch vigorous drives to highlight the issue. 

Investment minister Khalid Al-Falih was asked at a news conference if Saudi Arabia needs to try a different approach to overcome negative headlines, including over the murder of journalist Jamal Khashoggi and the imprisonment of critics in an ongoing crackdown.

In a country where it is rare for leaders to field this sort of question, the moderator asked the journalist to take the query elsewhere, but Mr Falih insisted on answering.

"Investors are not journalists, investors are looking for countries where they can place their trust in an effective government that has proper economic decision making," he said.

Some Western officials have indicated human rights will not be raised at the summit, saying they prefer to use bilateral forums to discuss the issue with Riyadh.

"Instead of signalling its concern for Saudi Arabia's serious abuses, the G20 is bolstering the Saudi government's well-funded publicity efforts to portray the country as 'reforming' despite a significant increase in repression," said Michael Page from Human Rights Watch.