China has offered $20bn (£12bn) in loans to African countries over the next three years, cementing an alliance that appears increasingly hostile to the west.

Hu Jintao, the Chinese president, promised the credit line – double the amount China pledged for the previous three-year period in 2009 – on Thursday during the opening ceremony of the Forum on China-Africa Co-operation in Beijing.

China's non-judgmental approach to business continues to gain traction with African governments, who say they will no longer tolerate being lectured by a hypocritical west that includes their former colonial masters.

Criticism that Africa is allowing its natural resources to be exploited, and that China is content to bolster dictators and ignore human rights abuses, merely feeds the partners' anti-western sentiment.

Hu brushed aside such concerns in his speech at the Great Hall of the People, attended by leaders from 50 African states including South Africa's Jacob Zuma and Equatorial Guinea's Teodoro Obiang Nguema, widely condemned by western activists as a brutal and corrupt dictator.

"China and Africa should increase co-ordination and co-operation in international affairs," Hu said. "We should oppose the practices of the big bullying the small, the strong domineering over the weak and the rich oppressing the poor."

He continued: "China wholeheartedly and sincerely supports African countries to choose their own development path, and will wholeheartedly and sincerely support them to raise their development ability."

China will "continue to steadfastly stand together with the African people, and will forever be a good friend, a good partner and a good brother", he added at the summit, which is held every three years since 2000.

Hu said the new loans would support infrastructure, agriculture, manufacturing and development of small and medium-sized businesses in Africa. He also pledged to "continue to expand aid to Africa, so that the benefits of development can be realised by the African people".

Africa is increasingly portrayed as a microcosm of the shifting global balance of power: three years ago China overtook the US as the continent's biggest trading partner.

Zuma did little to diminish the sense of rivalry with remarks that doubtless flattered his host.

"Africa's past economic experience with Europe dictates a need to be cautious when entering into partnerships with other economies," the South African president said.

"We are particularly pleased that in our relationship with China we are equals and that agreements entered into are for mutual gain. This gathering indicates commitment to mutual respect and benefit.

"We certainly are convinced that China's intention is different to that of Europe, which to date continue to attempt to influence African countries for their sole benefit."

China's alliance with Africa dates back to the 1950s, when Beijing backed liberation movements fighting to overthrow western colonial rule. In the past decade, China says its trade with Africa jumped from little more than $10bn (£6.35bn) in 2000 to $166.3bn in 2011, driven by Chinese hunger for resources and African demand for cheap Chinese products.

Western critics say China supports governments with dubious human rights records. The Asian country's biggest African trading partners in 2010 were Angola, ruled by one man for 33 years, South Africa and Sudan, whose president is wanted by the international criminal court.

China is also accused of importing labour to build roads and hospitals and extracting raw materials for processing at home, leaving little for local economies. During a visit to Zambia last year, the US secretary of state, Hillary Clinton, warned against a "new colonialism".

China bridles at such attacks and argues that China-Africa economic co-operation and trade now drives around a fifth of the continent's economic growth, while China has aided 600 infrastructure projects across the continent.

In a recent speech at South Africa's Institute of International Affairs in Johannesburg (pdf), the Chinese ambassador, Xian Xuejun, said: "Chinese and African people harbour simple but friendly sentiments towards each other. But there is a lack of in-depth understanding. Some western politicians and media also tend to make irresponsible remarks on China-Africa relations, attempting to mess up our co-operation."

Xian insisted that China has a "non-interference policy" with "no political conditions attached" because Africans know their own situation best.

"We have never pointed fingers to African countries concerning their independent and own choice of political system because we have never drawn lines according to ideological differences."

Chinese officials claim it is all about business. Gao Xiqing, the vice-chairman and president of the China Investment Corporation, the country's sovereign wealth fund that invests in more than 100 countries, said: "We grew up studying Karl Marx, Lenin, Chairman Mao. Karl Marx said the workers have no motherland and in fact today capital knows no boundaries of state. Wherever there's profit to be made, capital will go there. There's not that much difference for Chinese capital, as compared to any capital in the world."

But Gao said China still had a long way to go to rival western investment in Africa. "We don't compete with Americans," he told the New York Forum Africa conference in Gabon last month.

"If you count your investment as the percentage of the capital market, the United States accounts for almost half of all the world's capital markets, so how do you compete with that? Americans have been in this continent for a long time.

"Despite all the income investment in Africa, China only accounts for a few percentage points, whereas the western powers have been here forever and they account for more than 90%, especially the minerals and resources investments. So we don't compete; we come here to co-operate."