Dutch authorities started preparing on Saturday to tow away a vehicle-packed cargo ship which has been burning for days off the country's coast.

The operation of moving the Fremantle Highway from the Dutch coast, a UNESCO World Heritage site for the aquatic and terrestrial species it hosts, and closer to the north of Schiermonnikoog island temporarily aims to avert an ecological disaster.

However, later on Saturday evening, authorities said the operation would likely be delayed by several days, having initially said they hoped to start over the weekend.

What do we know about the towing operation?

The decision to proceed with moving the ship comes after the flames eating at it have significantly subsided.

"The temperature on board the ship has dropped sharply and the intensity of the fire and smoke development has decreased," said the Rijkswaterstaat, the national water management agency, in a statement.

The agency added that the cargo ship was also stable, "still intact below the waterline and does not tilt."

Shortly before 10 p.m. the Rijswaterstraat issued an update saying that southwesterly winds meant it had decided it was not yet safe to start the operation. 

It said that the current winds would "ensure that the smoke is drawn over the tugboat during the entire towing operation of the ship."

"So if the recovery company starts towing now, this is not without risks and the safety and health of the crew always comes first," the authority said, adding that it anticipated similar winds for the next few days. 

Fears for an ecological disaster

Efforts to put down the fire for the past few days were carefully calculated, and water had to be used comparatively sparingly for fear of sinking the ship and consequently prompting an ecological disaster. The ship was carrying 3,783 cars, including 498 electric cars, its Japan-based charter company K Line said.

Authorities feared the car parts, batteries and fuel would damage the ecologically sensitive site and harm its inhabitants.

Ship owner Shoei Kisen Kaisha suggested the fire started on one of the electric vehicles, whose lithium-ion batteries can be very difficult to extinguish, and can spontaneously reignite, after they catch fire or explode. The actual cause of the fire has yet to be confirmed.

The towing operation is expected to take around 12 hours.

The fire killed one member of the all-Indian crew of the ship.

rmt, msh/sri (AFP, dpa)