NATO Secretary-General Jens Stoltenberg on Friday stressed the need to beef up security along the alliance's northern flank to counter Russia, as he wrapped up a visit to Canada that included a tour of its Arctic defenses.

"The high north is strategically important for Euro-Atlantic security," Stoltenberg told a news conference at an air base in Cold Lake, Alberta, noting that with Finland and Sweden joining, seven of eight Arctic states will be NATO members.

"The shortest path to North America for Russian missiles and bombers would be over the North Pole," he also warned. "This makes NORAD's role vital for North America and therefore also for NATO."

NORAD is the North American Aerospace Defense Command, a US-Canadian organization.

The NATO chief and Prime Minister Justin Trudeau toured a Cold War-era early warning radar site, and observed Canadian Arctic military exercises.

Russia's capabilities in the far north "are a strategic challenge for the whole alliance," he said, citing a significant Russian military buildup in the region.

This includes, he outlined, the reopening of "hundreds of new and former Soviet era Arctic military sites," and its use of the high north "as a testbed for the most advanced weapons including hypersonic missiles."

Stoltenberg also expressed concerns about China's reach into the Arctic for shipping and resources exploration, with plans to build the world's largest icebreaker fleet.

"Beijing and Moscow have pledged to intensify practical cooperation in the Arctic. This forms part of the deepening strategic partnership that challenges our values and our interests," Stoltenberg said.

NATO, he said, must respond with an increased presence in the far north and investment in new capabilities.

He noted that climate change poses new "security challenges" that requires a fundamental rethink of NATO's Arctic posture.

"Climate change is making the high north more important because the ice is melting and it's becoming more accessible both for economic activity and for military activity," he explained.

Trudeau said Canada, which currently falls short on NATO spending targets, will soon be replacing its aging fighter jet fleet and modernizing its continental defenses in partnership with the United States.

Ottawa has earmarked billions of dollars for new satellites and undersea sensors in the Arctic, and the replacement of an aging network of radar stations from Alaska to Quebec that Trudeau said will "increase our abilities to detect and indeed deter threats coming across the pole."