The joint drills were initially scheduled for November 2025 but were postponed due to a clash with the G20 summit in Johannesburg.
A Russian warship arrived at a naval base off the South African coast on Friday to join Chinese and Iranian vessels in military exercises that risk further damaging Pretoria's relations with Washington.
A Chinese destroyer and replenishment ship and an Iranian forward base ship sailed into South African waters earlier this week ahead of the week-long manoeuvres due to start on Saturday.
China is the lead nation in the "Will for Peace 2026" drill involving navies from the 11-nation BRICS group, which US President Donald Trump has labelled "anti-American".
The South African navy said it would confirm details of the vessels present later on Friday.
The drills will allow the navies "to exchange best practices and improve joint operational capabilities, which contributes to the safety of shipping routes and overall regional maritime stability," South Africa's defence force said.
Russia and Iran have become close allies amid Moscow's ongoing all-out war in Ukraine, with Tehran providing drones Russia commonly uses in daily barrages against civilian and infrastructure targets across Ukraine.
Meanwhile, Washington this week seized a Russian-flagged oil tanker it said was part of a shadow fleet that carried oil for countries such as Venezuela, Russia and Iran.
It has also threatened action against Tehran should protesters be killed in mounting demonstrations sparked by anger over the rising cost of living.
The joint drills were initially scheduled for November 2025 but were postponed due to a clash with the G20 summit in Johannesburg.
Washington boycotted that summit amid a row with South Africa that includes anger over its ties with Russia and Iran.
In October, the Trump administration announced it was restricting the number of refugees it admits annually to 7,500 and giving priority to white South Africans.
The White House announced the programme in February, saying that the group faces discrimination and violence at home.
The country's government strongly denied that characterisation.
"We reiterate that allegations of discrimination are unfounded," South Africa's Ministry of Interior Relations said in May.
"It is most regrettable that it appears that the resettlement of South Africans to the United States under the guise of being 'refugees' is entirely politically motivated and designed to question South Africa's constitutional democracy."