"In the south, we will run out of food for 2 million people in a matter of weeks," Annan told delegates from 60 countries at a donors meeting in Oslo.
"If there was ever a time for donor countries to get off the fence, it is now," Annan said.
January's peace agreement ended the 21-year civil war in southern Sudan , opening the way for the country to receive badly needed funding for reconstruction.
The Oslo meeting brings together donor countries, international organizations and former enemies in the conflict who have joined a transitional team to create a joint government.
"The road to peace has been long and uphill," Norwegian Prime Minister Kjell Magne Bondevik said.
"We count of you to lead the reconstruction of areas devastated by war. Your people deserve it. They have waited too long to return to Sudan and live in peace."
Sudan hopes for pledges of EUR6 billion, said the Sudanese minister for international cooperation, Yusuf Suleiman Takana.
The conflict in southern Sudan was separate from the two years of bloodshed in the country's western Darfur region, where 180,000 people have died, according to U.N. estimates.
"The situation in Darfur remains extremely grave," said Annan. He said U.N. sanctions and potential war crimes charges against those responsible for the violence were made in the interest of peace.
"The measures are not aimed at the people or government of Sudan ," said Annan. "They target individuals responsible for heinous crimes."
In eastern Sudan , tribes and opposition activists have also clashed with government forces seeking greater rights and state assistance.
World Bank-administered funds would be launched at the conference for the new Government of National Unity in the Sudanese capital, Khartoum, and for the government of South Sudan , the Norwegian government said.
The peace treaty sets out power- and wealth-sharing rules, and calls for a referendum in six years on whether the south will remain part of Africa's largest country.
In the north-south war, Islamic-dominated Khartoum fought rebels seeking greater autonomy and a greater share of the country's wealth for the Christian and animist south. The conflict is blamed for more than 2 million deaths, primarily from war-induced famine and disease.
Norway had an active role in the Sudan peace process, and was asked in April 2003 to host the international donors conference.
The conference has drawn representatives of the United States and Canada; many European countries, including Germany, the U.K., Russia and France; such Asian powers as Japan and China; and African and Arab nations. Major organizations were also represented, including the European Union and the World Bank.
Sudan 's delegation was led by two Sudanese vice presidents, Ali Osman Mohammed Taha and former rebel leader John Garang of the Sudan People's Liberation Movement