Around 1 500 tonnes of chemicals on the NS Qingdao bulk carrier were being dumped into the sea about 250km off St Helena Bay in an operation expected to end in March, the SA Maritime Authority (Samsa) said on Thursday.

In October 2021, the ship was evacuated from the Port of Durban to St Helena Bay on the West Coast when rainwater set off a toxic fume chemical reaction.

The chemical cargo was apparently soaked by rain, causing it to become unstable and release the toxic fumes into the atmosphere.

A November 2021 statement by Samsa stated the NS Qingdao's cargo posed no danger to humans or the environment, but it could not immediately name the chemical when asked on Thursday.

"The vessel is currently anchored off St Helena Bay, and an emergency dumping permit has been obtained from the Department of Forestry, Fisheries and the Environment to dump the reacting cargo at sea," Samsa said in a statement.

St Helena Bay forms part of the important Benguela current system which recirculates water through upwelling, sustaining the health and nutrition of sea life and fish that fishermen and fishing companies rely on for survival.

Earlier statements said the chemicals would be neutralised and dumped ashore, but the new statement stated it will be dumped at sea depths of 3km.

"Red tide" alerts usually being in the area in January. Red tides bring a dense accumulation of microscopic algae to around 50km of the shoreline, which causes either toxicity for humans who eat fish contaminated by it, or to the sea life which consumes it. While being cleared, it can bring the local fishing industry to a standstill and deplete certain stocks, particularly rock lobster.

The chemical crisis work began with the ship being moved out of the Port of Durban with no structural damage, then moved to the site off St Helena Bay, with the vessel Umkhuseli on standby for safety, and hazardous materials specialists on site.

"To date, more than 1 000 tonnes of the cargo have been taken out of the vessel and it is expected that the remaining hotspots will be removed and dumped by 15 March 2022," said Samsa.

The ship sails under the flag of the Marshall Islands in the Pacific atoll and was built in 2011, according to marinetraffic.com.

During the looting and unrest in July 2021, a UPL warehouse was set alight in Cornubia, north of Durban.

In that instance, wetland and rivers were contaminated, tonnes of dead fish were removed by hazmat crews, and beaches were closed, amaBhungane and News24 reported.

The fire was eventually extinguished on 22 July, after 10 days, but chemicals had reached the Ohlanga River and the Umhlanga Lagoon.