The blaze burning on a cargo ship carrying thousands of vehicles off the coast of The Netherlands was losing intensity, authorities said Friday, as the fire spurs worries of damage to nearby natural sites.

An electric car is suspected of sparking the deadly blaze and officials said Friday that nearly 500 of the vehicles were aboard, far more than initially reported.

Fire broke out on the Fremantle Highway late Tuesday, killing one crew member, and prompting a massive effort to extinguish the flames.

"The blaze continues and there is still a lot of smoke," the Coast Guard said.

"But it indeed looks like it's losing intensity compared to yesterday (Thursday)," it added, saying the ship was still being kept outside busy shipping lanes.

Japan-based K Line, the ship's charter company, reported there were 3,783 cars on board the vessel when the blaze broke out -- far more than an initial estimate of around 3,000.

These were "all brand new/no used cars on board" including 498 "electrical vehicle units", the company told AFP in a statement.

Ship owner Shoei Kisen Kaisha said there was a "good chance that the fire started with electric cars", but added that the cause still needs to be investigated.

One sailor died after he and 22 others -- all from India -- were rescued from the burning ship that had forced some crew members to jump overboard.

The blaze on the Fremantle Highway has raised the specter of an ecological disaster on a nearby chain of islands, which include Terschelling and Ameland, where the fire was first reported.

The ship remained close to Terschelling and Ameland, which are part of an archipelago of ecologically sensitive islands in the Wadden Sea.

The area spanning the Netherlands, Germany and Denmark has been declared a UNESCO World Heritage Site and has a rich diversity of more than 10,000 aquatic and terrestrial species.

"It seems that the situation on the ship has stabilized somewhat," Heidi Bunicich, spokeswoman for the Ameland municipality told AFP.

"But of course we are very concerned. We have emergency plans in place to deal with various scenarios," she said on Thursday.