The annual G20 Summit opened here on Tuesday with world leaders set to discuss over the next two days challenges triggered by the Covid-19 pandemic and more recently topped by Russia's war in Ukraine.

Prime Minister Narendra Modi was welcomed at the summit venue by Indonesian President Joko Widodo, ahead of the formal opening of the summit.

"The Summit will witness extensive deliberations on ways to overcome important global challenges. It will also focus on ways to further sustainable development across our planet," the Prime Minister's Office tweeted.

He also briefly interacted with US President Joe Biden and French President Emmanuel Macron.

"Recover Together, Recover Stronger. Indonesian President @jokowi welcomes PM @narendramodi for the G20 Bali Summit. Detailed deliberations on contemporary global challenges including food & energy security and health are on the @g20org Summit agenda today," Spokesperson for the Ministry of External Affairs Arindam Bagchi said in a tweet.

In his remarks at the G2 Summit that began here on Tuesday, Indonesian President Widodo asked world leaders to follow the UN charter and called for an end to "the war", a reference to the Russia-Ukraine conflict.

He said all leaders have a responsibility towards the people of the world. Being responsible meant following the UN charter "consistently", he said.

"Being responsible means we must end the war," he said in the English portion of his brief opening remarks.

He did not name Russia or Ukraine in English but a part of his address to Group of 20 leaders was in Bahasa Indonesia.

It will be difficult to move forward if the war is not ended, he said, adding that the world must not slip into another Cold War.

Leaders from the world's major economies are set to discuss over the next two days challenges triggered by the Covid pandemic, topped more recently by Russia's war in Ukraine.

After the meeting in Indonesia, India will take over the Group of 20 presidency for one year.

'Recover Together, Recover Stronger' was the theme picked by Indonesia when it took charge last year. But the Russia-Ukraine war that began in February now threatens food and fuel shortages.

The leaders will hold three working sessions on food and energy security, digital transformations, and health. Modi is expected to participate in all three.

On the sidelines of the summit, Modi has bilateral meetings scheduled for Wednesday with Indonesian President Widodo, Spanish Prime Minister Pedro Sanchez, French President Macron and Singapore Prime Minister Lee Hsien Loong.

The list declared so far by Delhi does not mention Chinese President Xi Jinping, with whom Modi has not met face to face since the Galwan Valley clash between the troops from both sides in 2020.

There was no mention either of a separate meeting with Britain's new prime minister Rishi Sunak. But there is a possibility of more bilateral meetings being squeezed into the schedule.

The G20 comprises 19 countries: Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, South Korea, Mexico, Russia, Saudi Arabia, South Africa, Turkey, the UK, the USA and the European Union (EU).

Together, they account for over 80 per cent of the global GDP, 75 per cent of international trade and two-thirds of the world population.

A day ahead of the summit, US President Biden and his Chinese counterpart Xi met for three and a half hours in Bali, striking a conciliatory tone against the backdrop of a strain in their ties over self-ruled Taiwan.

Russian President Vladimir Putin has opted out of the Bali summit and sent foreign minister Sergei Lavrov to represent the country.

But western leaders who seemed to be preparing for a possible showdown over Russia's invasion of Ukraine are unlikely to back down. Russia can expect flak, for instance, when the summit discusses 'Food and Energy Security'.

Britain's new Prime Minister Sunak made his intention clear before leaving London for the meeting.

"This G20 Summit will not be business as usual," he declared.

There is also speculation over difficulties in drafting the summit communique, a consensus document, with the Ukraine issue becoming a stumbling block. There is also a possibility of Ukrainian President Vlodoymyr Zelensky virtually addressing the gathering.