When world leaders finally got together for the G20 summit in Rome after over two years apart, the mood was festive, with formalities temporarily ditched in favour of fist-pumping and football quips.

"It is great to see all of you here, after a difficult few years for the global community. The pandemic has kept us apart - as it did with all our citizens," Italy's Prime Minister Mario Draghi said Saturday in opening the two days of high-level talks.

Tempers could easily have frayed: ahead of the summit French President Emmanuel Macron had seriously fallen out with the US over a submarine deal, while tensions were escalating with the UK over fishing rights.

But Britain's Boris Johnson gave Macron a mock-combative fist pump as he showed up -- late -- for the group picture.

The Briton kept it informal with US President Joe Biden too, quipping "Hey Joe!" as he took his place.

In a first for a G20 "family photo", the leaders were joined by medics, firefighters and other front-line workers who saved lives during the coronavirus pandemic.

A White House official said the US and France had patched things up with the administration expecting future conversations to be "exciting and engaging".

Biden's wife Jill and Macron's wife Brigitte even grabbed a glass of wine together Friday, with Jill declaring they were "like sisters".

"I love Italy, Brigitte loves Italy. Who would not love Italy?" she said as they laughed together.

There was joshing around too between Argentine President Alberto Fernandez and Brazilian President Jair Bolsonaro -- who regularly clash over politics.

An informal, joshing atmosphere permeated the first in-person G20 summit in two years as leaders including US President Joe Biden, Turkish counterpart Recep Tayyip Erdogan and British Prime Minister Boris Johnson exchanged greetings
An informal, joshing atmosphere permeated the first in-person G20 summit in two years as leaders including US President Joe Biden, Turkish counterpart Recep Tayyip Erdogan and British Prime Minister Boris Johnson exchanged greetings POOL / KEVIN LAMARQUE

"You have not yet congratulated me for Argentina's triumph in the Copa America," Fernandez told Bolsonaro, who had publicly vowed Brazil would beat Argentina 5-0 in the final.

The Brazilian president had spent part of Friday living "la dolce vita" as he sampled delicacies near the Pantheon and posed for photographs at the Trevi Fountain, before posting a video of his jaunt on Twitter -- to the soundtrack of the Italian national anthem.

The leaders were set Saturday to dine with Italy's President Sergio Mattarella, who was laying on a feast of salmon, pumpkin risotto, stuffed artichokes and lashings of wine.

Their spouses had trips to the Colosseum and the Sistine Chapel at the Vatican planned first.

After a visit with the pope at the Vatican on Friday, the US motorcade -- made up of some 84 cars -- ran into trouble, with one of its vehicles caught up in a minor accident.

The White House said there were "no serious injuries".

The G20 has brought the historic city centre in the Italian capital to a standstill.

But a security "red zone" around the summit itself has left streets eerily empty around Rome's futuristic convention centre, known as the "Nuvola" (cloud), in the southern EUR district.

The neighbourhood, built by Benito Mussolini to glorify his fascist regime, certainly impressed Canadian Prime Minister Justin Trudeau, who remarked to Boris on the "unusual opulence" of the surroundings.

The Italian hosts certainly "have pushed the boat out", Boris quipped.

Across town, money -- or the lack of funds spent by the G20 on helping poor countries tackle climate change -- was the theme of a singing protest in Rome by an ABBA cover band.

It was not clear whether any of the leaders heard them.