JOHANNESBURG (AP) — South Africa’s trade minister has opened a summit of the BRICS emerging economies with a warning that the world’s trading system is enduring “enormous turbulence.”

Rob Davies on Wednesday referred to economic worries related to U.S. tariffs on goods from major trading partners and retaliatory action from those countries.

Davies calls it “a moment of crisis for the global multilateral trading system.”

Russian President Vladimir Putin, Chinese President Xi Jinping and other BRICS leaders from Brazil, India and South Africa plan to meet at the three-day summit in Johannesburg.

Ahead of his arrival in South Africa, Indian Prime Minister Narendra Modi was in Uganda, where he pledged to deepen India’s engagement with Africa.

Turkey’s president, Recep Tayyip Erdogan, is also invited to the BRICS meeting.