Relief as stranded ship docks in Sydney

A Hong Kong cargo ship that was left stricken in heavy seas off the coast of NSW has docked safely in Port Botany after a multi-day operation to the relief of the crew on board.

The bulk carrier Portland Bay was towed into Botany Bay in Sydney's south on Wednesday afternoon following an order from the Australian Maritime Safety Authority (AMSA) for it to be brought to port.

Other commercial shipping operations were suspended as four tugboats towed the powerless vessel through windswept waters.

The 170-metre Portland Bay, with a crew of 21 led by a Ukrainian captain, had been floating south of Sydney after the ship's engines failed on Monday.

AMSA on Wednesday ordered the ship be towed to port in a legal direction to its master and the salvage team.

"It is vital that the vessel be moved into safe harbour before the next front of bad weather arrives," executive director Mark Morrow said in a statement.

Ports Authority NSW chief executive Philip Holliday said the co-ordinated response and winds slowing to 20 knots helped the towing operation.

"Relief is a really good word," he told reporters after it docked safely.

"The fact that we're here talking about the vessel being safely alongside is a credit to everyone that's been involved, including the ship's crew."

AMSA took over as lead agency from the NSW Port Authority for the incident and will send inspectors to assess the vessel's mechanical safety and compliance.

Initial plans to pull the boat to deeper water were scuppered by severe weather, resulting in towing lines breaking.

Tugboats managed to move the Portland Bay further north and it dropped anchor about 1.2 nautical miles from Port Botany.

A turbo fan is believed to be responsible for the engine failures and the problem will take about half a day to fix.

AMSA and the Australian Transport Safety Bureau will investigate the incident.