South Africa's trade minister Parks Tau said on Sunday that he expected negotiations with the US over a trade deal would continue, despite differences between the two countries over this weekend's Group of 20 summit in Johannesburg.

Host nation South Africa pushed through a G20 Leaders' Declaration at the summit despite objections from the US, which boycotted the event.

"We've compartmentalised these issues and said the G20 is a separate process, ... we anticipate that the trade discussions will continue," Tau told reporters at the summit.

South Africa's efforts to secure a trade agreement with the US have been complicated by issues including Trump's unfounded accusations of persecution of South Africa's white minority.

Trump imposed a 30 per cent tariff on imports from South Africa in August, which could cause tens of thousands of job losses at a time Africa's biggest economy is barely growing.