Before the talks, the leaders had said that climate change, the economy and Africa would be the priorities at the L'Aquila gathering.
Charity workers have already expressed disappointment at what they see as broken promises from leaders, after Italy announced a 56 per cent cut in its aid budget this year.
Meredith Alexander from Actionaid told Al Jazeera there was a "division in the pack", with the UK on target to meet their aid pledge, while Italy is "moving backwards".
She also critised Italy for "absconding from the debate" on aid and food security, saying it had "refused to take the kind of leadership that the G8 is expected to show".
"But [Barack] Obama has stepped in and he's stepped in on the right issue. A billion people go hungry every single day and it's absolutely time for world leaders to focus on this," she said.
Adrian Lovett from the charity Save the Children also expressed anger over Italy's cuts to aid.
"It's hard to see how that counts as leadership at a critical moment for the world's poorest people," he told Al Jazeera.
"This economic crisis means that perhaps 400,000 children could die ... because of the lack of support they'll receive while world leaders are looking elsewhere," he said.
A heavy security presence is surrounding the converted police barracks where talks are taking place, with about 15,000 police officers and soldiers deployed in L'Aquila and Rome.
Officials are hoping to prevent a recurrence of the violence seen during the country's last G8 meeting in 2001.
|Thirty-six people were arrested in the Italian capital in protests on the eve of G8 [AFP]
Despite this, protesters are continuing to gather, with more than 100 Greenpeace activists from around the world occupying four coal-fired power stations across Italy to demand action on climate change.
In Rome, activists from Oxfam International staged a mock gathering of world leaders in an event designed to highlight climate change.
Environmentalists also protested on the Spanish Steps in the capital, stripping off some of their clothes and raising a banner calling on leaders to "keep climate cool".
Three people were briefly detained by police, the AP news agency reported.
On Tuesday, 36 protesters were arrested in Rome, after protesters hurled bottles at riot police and set fire to tyres in the streets.
Silvio Berlusconi, Italy's prime minister, moved the G8 venue from Sardinia to L'Aquila, where more than 250 people died in an earthquake which struck the town in April. The premier believes hosting the summit in L'Aquila will help to rebuild the area.
Officials have drawn up plans to evacuate the leaders and cancel the summit if any tremor measuring more than four points on the Richter scale is felt.