Meanwhile Barack Obama, the US president, has arrived in Italy for attending the summit.
Al Jazeera's Alan Fisher, reporting from L'Aquila, said there have already been disappointments on some issues G8 leaders were hoping to tackle, including climate change.
"They say that they won't be able to get the emerging nations to agree to climate change figures by 2050, and that was always likely to happen," he said.
"There's still a lot of negotiations to go but I think the G8 were hoping they could do some of the groundwork before the big climate conference in Denmark in December."
He added that talks on aid will also be significant, after leaders pledged in 2005 to increase aid and trade, and in Italy, which has cut its aid budget.
Adrian Lovett from Save the Children charity told Al Jazeera that G8 leaders have not kept their promises on aid.
"It was really disappointing and frankly a disgrace to hear Italy's confirmation in the last 48 hours that they will cut aid not only this year but also next year as well.
"It's hard to see how that counts as leadership at a critical moment for the world's poorest people.
"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 a converted police barracks where the talks would take place, and around 15,000 police officers and soldiers have been 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.
Despite the police presence, 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.
On Tuesday, some 36 protesters were arrested in Rome, after protesters hurled bottles at riot police and set fire to tyres on the streets of the capital.
Silvio Berlusconi, Italy's prime minister, moved the G8 venue from Sardinia to L'Aquila, where more than 150 people died when an earthquake struck the town in April, in order to help 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 strikes the region.