Two Norwegian helicopters and several vessels have been searching the area since Thursday, and more help was on the way.
Two Norwegian helicopters and several vessels have been searching the area since Thursday, and more help was on the way, including a coast guard vessel and a sea patrol plane, the head of the rescue operation Tore Hongset told AFP.
A small robot submarine was deployed overnight to investigate an area where an oil patch and bubbles were observed, but "it hasn't yielded any results yet," Hongset said.
The aircraft, a Russian Mil Mi-8, went down in the afternoon two or three kilometres from Barentsburg, a Russian mining community in the archipelago.
Its eight occupants, five crew and three scientists, were all Russian nationals.
"The chances of finding people alive fade considerably over time," Hongset said.
"But we're continuing. This morning, we're maintaining our search for possible survivors, who could be on a floating object such as a survival raft."
Norway was afforded sovereignty of Svalbard, located around 1,000 kilometres (620 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, a community home to several hundred Russian and Ukrainian miners.
In 2008, another Mil Mi-8 crashed near Barentsburg, killing three of its nine occupants. Yet another crash near Pyramiden of the same type of helicopter left two dead in 1991.