Chinese President Hu Jintao made the announcement in Beijing at the fifth ministerial conference of the Forum on China-Africa Cooperation attended by heads of state and ministers from 50 African countries. At the previous summit in 2009, China had pledged $10 billion in so-called soft loans.
Hu said his government will take measures in priority areas to support development in resource-rich Africa and boost the China-Africa strategic partnership, the official Xinhua news agency reported.
"China will provide $20 billion in credit to African countries to assist them in developing infrastructure, agriculture, manufacturing and small- and medium-sized enterprises," Hu said.
Hu said China's trade and investment in Africa have been expanding. In 2011, two-way trade reached $166 billion and Chinese direct investment in Africa has exceeded $15 billion, with investment projects covering 50 countries.
Africa's exports to China have largely consisted of raw materials, while Chinese exports have been largely manufactured goods such as electronics. This has raised criticisms that China is exploiting Africa's natural resources.
The New York Times said China's aid to Africa has expanded greatly while the continent had become a major provider of resources for China, such as oil from Sudan and Angola and copper from Zambia and the Democratic Republic of Congo.
The Times said among criticisms are that China provides aid without taking into consideration issues such as human rights performance and governance, as in Sudan. China is also seen as using its infrastructure projects such as roads and ports to benefit its own industries.
While praising China's involvement in Africa at the meeting, South African President Jacob Zuma was quoted as saying Africa's commitment to China's development has been demonstrated by supply of raw materials, other products and technology transfer, noting such trade pattern "is unsustainable in the long term."
Hu promised China would train 30,000 Africans, offer 18,000 scholarships and send 1,500 medical personnel to Africa. He said China would also help improve drinking water and protect forests.
Li Xinfeng, an African studies scholar at the Chinese Academy of Social Sciences, told the Times, "Before, China had more of an attitude that 'We'll give what we want to give you,' but now the aid is more focused on African needs."