U.S. Secretary of State Hillary Clinton flew to Tromsoe in the Arctic Circle to see first hand the way climate change is opening a once frozen region to competition for vast oil reserves, according to AFP.

Experts here estimate the value of the Arctic's untapped oil alone - not including natural gas and minerals - at $900 trillion, making it a huge prize for the five countries that surround the Arctic if they can reach it.

And with climate warming opening up some 46,000 kilometers a year that had once been bound in ice, the region is expected to burst open, not just with oil exploration but with East-West trade along a more accessible northern route.

"We believe strongly it's important for the five principal Arctic nations to begin working together to make plans for what will almost certainly become greater ocean travel, greater exploration, therefore greater pollution, greater impact of human beings," Clinton said.

The Arctic was a key subject of Clinton's discussions in Oslo with Norwegian leaders who have been among the first to recognize the changing outlook for what they call the "high north."

"I think we both feel we have a very important obligation to get ahead of that and to prepare for what is likely to come," Clinton said at a news conference with Foreign Minister Jonas Gahr Stoere.

She is taking a tour on a research vessel Saturday to see the effects for herself, in the area around Tromsoe, a city of 70,000 on an island surrounded by snow covered ridges where the sun never sets at this time of year.

It has become a center for research on the Arctic and climate change, and is the headquarters of the Arctic Council, a five nation advisory body that makes recommendations on the management of the Arctic.

Studies have found that between 1979 and 2007, the Arctic's expanse of ice in the warmer summer months has decreased by 45,000 square kilometers per year.

Despite worries that a thawing Arctic could set off a "great game" among powers seeking to carve out their slice of undersea riches, experts here say that under the Law of the Sea only five countries can lay claim to most of the Arctic. They are Russia, which has about half the Arctic coastline, Canada, Norway, Denmark and the United States.