Situated halfway between the European continent and the North Pole, the region around Svalbard has gained in geopolitical and economic importance as tensions mount between Russia and the West, not least with the ice sheet receding.

Interest in the Arctic has intensified since US President Donald Trump's threats this year to annex Greenland, which he says the US needs for reasons of national security.

"It was especially appropriate to come this year," the 88-year-old monarch said after stepping off the royal yacht with his wife Sonja in Longyearbyen, Svalbard's main town which is home to 2,500 people.

"We have seen increased attention being paid to the Arctic and Svalbard. This brings both challenges and opportunities," he added.

The king was in Svalbard to take part in celebrations marking the 100th anniversary of the entry into force of an international treaty that put the Svalbard archipelago under Norwegian rule.

Drawn up in Paris in 1920, the treaty gives the citizens of the nearly 50 signatories -- including China and Russia -- an equal right to exploit the archipelago's natural resources.

As a result, Russia is able to maintain two settlements, including a mining community, in the small village of Barentsburg where a Lenin statue stands and Soviet flags are regularly flown -- all in a NATO country.

China has meanwhile defined itself as a "near-Arctic state" and has displayed a growing interest in the region.

"When the royal yacht 'Norge' drops anchor with the royal standard atop the mast, this emphasises, even more than King Harald's words could say, that Norway is taking care of its rights and assuming its responsibilities," said Lars Nehru Sand, a commentator at public radio NRK.

"The king is here to show that this is ours," he said.