South African ports will be able to cope with swelling numbers of ships rounding the Cape as they seek to steer clear of pirate-infested waters off the Somali coast and stand to benefit from increased business, the National Ports Authority has said.

But the authority did not expect a sudden deluge of ships and the situation would not cause the congestion last seen in the 1970s when the Suez Canal was shut because of conflict in the Middle East, said spokesperson Koen Birkenstock.

The risk to shipping from piracy off the Somali coast, with a drop in the price of bunker fuel after easing international crude oil prices, could increasingly entice ship owners to opt for the Cape sea route rather than Suez and the Gulf of Aden, Birkenstock said.

The danger of losing a ship, and its cargo, higher insurance costs and concerns over the safety of seafarers would weigh heavily on the higher-profile shipping companies and make it easier for them to choose the longer route around the Cape, he said.

That risk had to be measured against not only the cost of more fuel to cover the greater distance around the Cape, but also the cost of time in terms of days lost getting cargo between European and Asian destinations.

A prominent Norwegian shipping company, Odfjell SE, said it made the decision to divert its ships after pirates seized the Saudi Arabian supertanker MV Sirius Star, hundreds of kilometres off the coast of Kenya in the most brazen attack yet by Somali pirates.

At least three big shipping companies, the world's largest tug operator Svitzer and a large liquefied petroleum gas operator have said they are also avoiding the Suez.

But three of the Middle East's top oil exporting nations, Saudi Arabia, Iran and Kuwait, have no immediate plans to alter their crude oil shipping operations despite an increased threat from pirates off East Africa.

The Gulf of Aden, off Somalia, is linked to the Red Sea, which in turn is linked to the Mediterranean by the Suez Canal.

The route is thousands of kilometres and many days shorter than going around the southern tip of Africa.

"This will incur significant extra cost, but we expect our customers' support and contribution," Storeng said.

The ports authority's Birkenstock and salvage expert David Main, of Smit Marine South Africa, said the local industry was capable of dealing with an increase in shipping and had the capacity to provide services.

"I don't see a lot of extra cargo-discharging or loading happening here," Main said.

"Cargo facilities will not be the issue. If they stop here, it would be for the convenience of bunkering (refuelling).

The one thing that may be against us is the fact that, in Cape Town, ships have to berth to bunker. They cannot bunker at a pipeline in the bay."

Birkenstock said ships would be able to bunker from quayside points at four berths in Table Bay Harbour - two on the landing wall and two at the eastern mole.

Ships would also be able to get bunkers from the port's bunker barge if they were forced to dock at cargo docks.

"If there is an overrun here, ports such as Port Elizabeth, Durban and Richard's Bay can also provide services - such diversions would be dealt with by shipping agents," he said.

Main said "shipping companies have begun to pay crews double time if they are routed along the Somali coast".

He said an increase in shipping around the Cape coast would invariably also lead to a great demand for services and an increase in incidents out to sea could also not be discounted.

"It is true that the Cape sea route also has less friendly weather and sea conditions," he said.