Hairline cracks had appeared on the main deck of the bulk carrier Seli 1, which is grounded in Table Bay, authorities said on Wednesday.

The cracks were being monitored daily by the salvage team on board, the South African Maritime Safety Authority (Samsa) and salvors Smit Marine said in a statement.

If left unattended, the cracks "could have a negative influence on the structural integrity of the vessel".

A naval architect was designing strengthening measures, which would be welded into place as soon as weather permitted.

"No vessel is designed to withstand the impact of grounding forces for a prolonged period of time," said Samsa and Smit Marine.

"Further deterioration will depend entirely on the relevant flexing of the vessel and conditions that the vessel is subjected to."

The ship's cargo of 30 000 tons of coal remained on board.

Samsa was still trying to finalise legal and logistical requirements for removing the cargo, for which a cost-effective plan had already been drawn up.

The Seli 1 went aground on Table View beach in a gale on 8 September.