OSLO - A Russian helicopter that went down off the coast of Norway's Svalbard archipelago in the Arctic this week has been found and the eight Russians on board are presumed dead, Norwegian rescue crews said on Sunday.

The Mil Mi-8 chopper, carrying five crew and three scientists, went missing on Thursday as it was flying to Barentsburg from Pyramiden, a former mining community in Svalbard that is now a tourist site.

It went down two or three kilometres from Barentsburg, a Russian mining community in the archipelago.

"The wreck of the Russian helicopter has been located... northeast of Heerodden, at a depth of 209 metres (686 feet)," the rescue services said in a statement.

"The search has now concluded, and has moved into a search phase for the presumed dead."

A sea patrol plane, a Danish aircraft, two Norwegian helicopters and several vessels had been searching the area since Thursday.

No contact had been made with the chopper before or after it went down.

A small robot submarine located the wreck after investigating an area where an oil patch and bubbles were observed, rescue services said.

The cause of the crash was not immediately known, but visibility in the area was reduced because of snow and darkness, which falls early this time of year at this latitude.

Norway was afforded sovereignty of Svalbard, located around 1,000 kilometres (600 miles) from the North Pole, under the 1920 Treaty of Paris.

Nationals of all signatory states enjoy "equal liberty of access and entry" to Svalbard and its waters.

As a result, Russia operates a coal mine in Barentsburg, home to several hundred Russian and Ukrainian miners.

According to Russia's consul general in Svalbard, Viacheslav Nikolayev, the helicopter was owned by the Arktikugol coal mining company and was used regularly to fly the miners between Barentsburg and Svalbard's main town of Longyearbyen.