Two more sperm whales became stranded and died on the Dutch coast a day after five others, likely from the same pod, lost their lives nearby in a rare North Sea beaching, experts said on Thursday.

"They are two males," said Jan Boon from the Royal Netherlands Institute for Sea Research (NIOZ), which is based on the northern Dutch island of Texel where the whales washed up.

One was found near the Texel port in front of NIOZ's buildings in the village of 't Hoorntje, while the other became stranded further to the north.

"The one I've seen here in the south has unfortunately been dead already for some time," Boon told AFP.

"There's blood, it's mouth is open," he said.

The two whales and the five others that died on Wednesday after floundering ashore late Tuesday are "probably from the same pod of six whales" that came ashore in Germany earlier this week.

Sperm whale beachings in the Netherlands are relatively rare with one incident annually between 2011 and 2014, while four whales beached in 2004 and five in 1997.

"A group like this is even rarer," said Boon, adding the North Sea is too shallow for the large, deep-diving animals.

The sperm whale is the largest of the toothed whales, and the largest toothed predator. It can measure up to 20 metres (67 feet) long and weigh over 50 tonnes.