JOHANNESBURG—China’s President Xi Jinping on Friday pledged $60 billion in financing for development across Africa, aiming to reaffirm his country’s commitment to the continent despite the economic turmoil caused by slowing growth of the world’s second-largest economy.

Mr. Xi told dozens of African leaders at a summit in Johannesburg the funds would be invested in 10 projects over three years. The Chinese leader didn’t specify which of Africa’s more than 50 countries would receive the aid.

“These plans are aimed at addressing three issues holding back Africa’s development,” Mr. Xi said to warm applause from the presidents and prime ministers of Africa’s largest economies. “Namely inadequate infrastructure…professional and skilled personnel, and funding.”

Friday’s pledges represent nearly a doubling of the three-year, $30 billion funding package that China announced in 2012, said Kai Xue, a Beijing-based lawyer who advises Chinese businesses operating in Africa.

China’s broader trade relationship with Africa has grown even more rapidly, to $222 billion last year—a record that made China the continent’s top trade partner for the sixth straight year. As a result, many African countries have forged deep diplomatic ties with Beijing and praised China’s authoritarian model of economic development.