South Africa's G20 presidency this year will prioritise efforts to help developing countries finance their shift to a low-carbon economy, President Cyril Ramaphosa said, even as the United States radically scales back its support.

Finance ministers and central bank chiefs from the Group of 20 developed and developing nations have gathered in South Africa for a two-day meeting.

The Treasury secretary is the second top U.S. official not to attend the Group of 20 gatherings because of rising tension with South Africa over its land policies.

President Cyril Ramaphosa has formally opened the G20 Finance Ministers, and Central Bank Governors' meeting in Cape Town this Wednesday 26 February.