The world has "failed to ensure food security", France's agriculture minister has said at the UN food agency crisis talks on East Africa's drought.
"If we don't take the necessary measures, famine will be the scandal of this century," AFP news agency quotes Bruno Le Maire as saying in Rome.
More than 10m people are thought to be at risk of starvation and famine has been declared in two areas of Somalia.
Ahead of the summit, the World Bank pledged $500m (£307m) to help.
Some $12m will be for immediate assistance to those worst hit by what the UN says is East Africa's worst drought in 60 years.
But the bulk of the money will go towards long-term projects to aid livestock farmers.
UN chief Ban Ki-moon has urged donor nations to supply an extra $1.6bn in aid.
Earlier the Red Cross said it had delivered food to one of Somalia's worst-hit areas, which is controlled by Islamists.
Working through a local committee, the Red Cross delivered food for 24,000 people by lorry.
'Question of life and death'
Al-Shabab, an al-Qaeda-affiliated group which controls large swathes of south and central Somalia, had imposed a ban on foreign aid agencies in its territories in 2009, but has recently allowed limited access.
But the World Food Programme says it still cannot reach 2.2 million people inside Somalia as refugees continue to pour over the Kenyan and Ethiopian borders.
Somalia is thought to be worst-hit by the crisis, but Ethiopia and Kenya have also been affected.
Analysts say the drought has been caused by the lack of rains and the failure of governments to adequately finance agriculture and irrigation schemes.
The meeting of ministers from the G20 nations at the UN's Food and Agriculture Organisation headquarters in Rome was requested by France, the current chair of the G20 group of powerful economies.
"Our meeting is a question of life or death for tens of thousands of people," Mr Le Maire said at the start of the meeting, AFP reports.
Bob Geldof and other celebrity activists are urging the international community to come up with more cash.
They accuse some countries - Italy, France, the Arab states and Germany - of contributing too little in proportion to their national wealth.
Mr Le Maire told the BBC said the first aim of the meeting was to co-ordinate the aid and response to the crisis.
"The second goal is also to think about the future and the long-term perspective because what we see here in Africa is that people need to have their own food and to have their own agriculture," he said.
BBC Africa analyst Martin Plaut says many people at the heart of the current disaster - in Ethiopia - have emerged relatively unscathed.
This is because the government in Addis Ababa has such an extensive safety net in place, he says.
Pre-positioned supplies mean the Ethiopian authorities could respond rapidly once the extent of the drought became clear.
The first food distributions began in February and have continued to the worst effected communities across a vast area.
Communities are suffering, but the famine that has hit neighbouring Somalia has so far been avoided in Ethiopia and overall the disaster management system, built up since the 1980s, has worked.