South African President Cyril Ramaphosa is the "last hope" for Africa's most advanced economy, but his government must turn incentive policies into laws to secure more Chinese investment, a senior Chinese diplomat told Reuters.

China is South Africa's largest trading partner and has pledged more investment than any other country since Ramaphosa embarked on a drive last year to attract $100 billion of new investment to lift the economy out of a slump.

While it has attracted some $55 billion in total pledges - including from Saudi Arabia and the United Arab Emirates as well - the drive has so far done little to ease crippling unemployment or boost economic growth.

"President Cyril Ramaphosa is the last hope of this country," Lin Songtian, China's ambassador to South Africa, told Reuters.

But while African nations have seen a boom in infrastructure development over the past decade, he said projects proposed by the South African authorities had lacked feasibility studies capable of reassuring the Chinese government and banks of their profitability and sustainability.

Policies of extending incentives, including tax breaks, to attract foreign capital also did not do enough for Chinese investors, who Lin said wanted to see favourable conditions enshrined in an investment law approved by parliament.