The Japanese Government hosting the event had hoped that the summit would focus on climate change.
But as negotiations got underway, charities warned world leaders not to renege on their commitments to Africa.
They fear that the world's leaders will try to pull back from commitments made at the Gleneagles G8 summit in 2005 to increase aid to developing countries by $50 billion by 2010. Half of this would go to Africa.
Against a backdrop of economic uncertainty, development agencies think that world leaders will cite the financial slowdown as a reason for pulling out of its commitments.
Although the UK is currently on track to meet its commitments to Africa, France and Italy seem to be keen to break previous promises to increase aid.
"High food and fuel prices are crippling for those who already live a hand to mouth existence," said Tearfund's Peter Grant. "This is not the time to step away from hard fought commitments to help the world's poorest people."
Oxfam warned that the G8 nations were likely to miss their promise to increase aid by $50bn by up to $30bn. This could cost up to 5 million lives, it said.
"For rich countries, $50 billion is pennies, for Africa this is life and death," said Oxfam's Max Lawson.
"There is a moral reason why we can't allow high food and oil prices to undermine our work in Africa," added Oliver Buston from Bob Geldof's One campaign. "Africa can become a serious producer of food and can help us in bringing down food prices."
With the UN Security Council due to discuss further sanctions against Zimbabwe tomorrow, it is expected that the G8 will make a statement on the crisis over the next three days.
Speaking from Zimbabwe, a spokesman for the Zimbabwe Christian Alliance said, "We call on the G8 leaders to leave no stone unturned in their efforts to address the double disaster of the political and humanitarian crises in the country.
"Our people are suffering terribly, but the ongoing violence is preventing us from reaching those who are in desperate need."
An announcement on the G8's aid to Africa is due to be made later this week.