Angela Merkel, the German chancellor, said: "The African countries expressed their fears that many of the Millennium Development Goals will be more difficult to reach if commodity prices keep rising like they are at the moment."
The call to assist Africans in need came as Jean Ping, the African Union's senior diplomat, was taken to hospital in the city of Sapporo, Japanese officials said.
The three-day summit also discussed the impact of food prices, which have nearly doubled in three years, setting off riots in parts of the developing world. These areas are also hardest by record oil prices.
Ban Ki-moon, the UN secretary-general, who attended the start of the summit, backed the African leaders and called on the G8 to live up to its Millennium Development Goals to double aid for Africa by 2010.
It was initially promised in 2005, at a summit in Gleneagles, Scotland, to double aid to Africa to $25bn a year by 2010 as part of a wider drive to alleviate global poverty.
Ban said: "The world faces three simultaneous crises - a food crisis, a climate crisis and a development crisis," Ban told reporters. "The three crises are deeply interconnected and need to be addressed as such."
However, the G8 countries have been accused of backtracking.
|What is the G8?
The G8 nations are the US, UK, Canada, France, Italy, Germany, Russia and Japan.
G8 concept first emerged in mid-1970s as informal forum for the world's leading industrialised democracies when it had just six members (the G6).
Canada joined the group in 1976 and the group became the G8 when Russia formally joined in 1997.
Group has rotating presidency responsible for planning and hosting annual meetings. This year Japan chairs the meetings.
In 2005 five outreach countries were added to the forum (the G8+5), representing five leading emerging economies: Brazil, China, India, Mexico and South Africa.
Ayesha Kajee, programme director of the International Human Rights exchange, told Al Jazeera that the G8 has achieved little to alleviate Africa's problems.
She said: "Well if one uses Gleneagles as the baseline, then very little has been done to fulfil the promises made there in 2005, given that $25bn was promised to Africa over fives years to 2010, very little of that has materialised, and been seen by Africans.
"On the other side of that coin, African leaders do understand that they are being held to so-called 'good governance' standards.
"However, many feel that is quite unfair to hold them to these standards, considering, for example, the record of good governance displayed by the current administration in the United States.
"Many also think that it is unfair that Africa's problems be focused primarily on Zimbabwe. Yes, there is a crisis there, but there are many other problems surrounding issues of food security that are effecting other parts of this continent," she said.
Jesse Griffiths, a policy adviser at ActionAid, told Al Jazeera that the manner in which the G8 delivers aid is "scandalous".
He said: "Much G8 aid is tied to the goods and services of G8 countries."
"If G8 leaders and their countries were to untie all their aid, there would be a cost saving of over $6bn."
UN and African Union figures indicate that less than a quarter of the pledged amount has been forthcoming.
Last month, a report by the Africa Progress Panel, a group set up to monitor implementation of the Gleneagles plan, said that under current spending the G8 will fall $40bn short of its target.
'Watered down' pledges
The report was rebutted by Japan's foreign ministry on Sunday, which denied the G8 was failing to deliver on its promises.
Kazuo Kodama, a Japanese foreign ministry spokesman, said the report was "completely false and unfounded", although he acknowledged that Africa was well behind target on health.
Oxfam, a British charity and advocacy group, said G8 members were instead trying to water down a pledge made at last year's summit in Germany to meet the Gleneagles goals.
Max Lawson, a policy adviser to Oxfam, said the Hokkaido summit was arguably the most important G8 gathering in a decade.
"The world is clearly facing multiple crises - serious, serious economic problems, both rich and poor countries. But it is poor people who suffer the most, suffering hugely from food price increases," he said.
A preliminary World Bank study released last week estimated that up to 105 million more people could drop below the poverty line due to rising food prices, including 30 million in Africa.