The cost of the damage caused by an explosion at an Amanzimtoti container depot is over R60-million, a spokesperson said on Monday.

"Over 70 steel containers and about 100 refrigerated containers were damaged. The total damage is over R60-million," said SATI's Jayson Naidoo.

On Sunday, four men were injured when the 23 000 litre oil tank exploded at the SATI container services plant in Ezimbokodweni industrial area, sending plumes of thick black smoke into the air.

Naidoo said the cause of the explosion was still not known and forensic experts would visit the scene on Tuesday to try to shed light on the cause.

One man's face and legs were burnt during the incident and he was admitted for medical treatment.

KwaZulu-Natal economic development MEC Mike Mabuyakhulu visited the scene on Monday to asses the extent of the damage and to see if the company needed government help.

"As the department that is responsible for economic development, we take a keen interest in what is happening which may have an impact in our economy," said Mabuyakhulu after he saw the extent of the damage.

He said he was worried when he heard about the accident as many of South Africa's imports and exports were handled in KwaZulu-Natal.

"We are very pleased as government that although the damage is huge, the depot is still operating.

"We are also pleased that the company is busy cleaning the spillage to ensure that there is no ecological disaster," he said.

The explosion was so violent that it cracked the windows and roofs of nearby companies.

Although the fire was extinguished on Sunday, firefighters were still monitoring the situation on Monday as the exploded tanker was still warm.

"Firefighters are still on the scene, ensuring that no fires would occur. They managed to stop the fire. It is still unknown on what could have caused the blast," said police spokeswoman Senior Superintendent Joyce Khuzwayo.

"They are also looking for clues to give direction of what could have caused the fire," she said.