Russian explorers have planted their country's flag on the seabed 4,200m (14,000ft) below the North Pole to further Moscow's claims to the Arctic.
They were travelling aboard two mini-submarines on what is believed to be the first expedition of its kind.
Having planted the rust-proof titanium metal flag, the explorers will collect scientific samples and begin the risky journey back to the surface.
Melting polar ice has led to competing claims over access to Arctic resources.
Russia's claim to a vast swathe of territory in the Arctic, thought to contain oil, gas and mineral reserves, has been challenged by other powers, including the US.
The mission's leader, explorer and parliamentarian Artur Chilingarov, told Itar-Tass news agency that his mini-submarine had a "smooth" landing on the seabed.
"The yellowish ground is around us, no sea dwellers are seen," he said.
'Heroic mission'
The mini-submarines, Mir-I and Mir-II, were brought to the North Pole by the two ships in the Russian expedition - a nuclear-powered ice-breaker and a research vessel.
 It's a very important move for Russia to demonstrate its potential in the Arctic... It's like putting a flag on the Moon
Sergei Balyasnikov
Russian Arctic and Antarctic Institute  
The expedition set off last week from the port of Murmansk in search of geological evidence to back up Moscow's claims to the resource-rich Arctic seabed.
Scientists aboard the submarines also plan to collect samples of Arctic flora and fauna.
Russian media reported last week that the ships were briefly tailed by foreign aircraft, but this claim was played down by the expedition leader.
Itar-Tass reported on Wednesday that the expedition's ships had arrived at the North Pole.
The submarines' return from the seabed to the surface is regarded as the most dangerous part of the journey.
The vessels will have to navigate back to the exact point where they started from, or else risk being trapped beneath the Arctic ice.
"This is a risky and heroic mission," Sergei Balyasnikov, a spokesman for Russia's Arctic and Antarctic Institute, told the RIA-Novosti news agency.
"It's a very important move for Russia to demonstrate its potential in the Arctic," he said. "It's like putting a flag on the Moon."
Competing claims
President Vladimir Putin has already described the urgent need for Russia to secure its "strategic, economic, scientific and defence interests" in the Arctic.
Moscow argued before a UN commission in 2001 that waters off its northern coast were in fact an extension of its maritime territory.
The claim was based on the argument that an underwater feature, known as the Lomonosov Ridge, was an extension of its continental territory, but it was rejected and Russia told to resubmit with more evidence.
Several countries with territories bordering the Arctic - including Russia, the US, Canada and Denmark - have launched competing claims to the region.
The competition has intensified as melting polar ice caps have opened up the possibility of new shipping routes in the region.
Current laws grant countries an economic zone of 200 nautical miles beyond their land borders.
This zone can be extended where a country can prove that the structure of the continental shelf is similar to the geological structure within its territory.
The North Pole is not currently regarded as part of any single country's territory and is therefore administered by the International Seabed Authority.
RUSSIA'S ARCTIC CLAIM
1) North Pole: Russia leaves its flag on the seabed, 4,000m (13,100ft) beneath the surface, as part of its claims for oil and gas reserves
2) Lomonosov Ridge: Russia argues that this underwater feature is an extension of its continental territory and is looking for evidence
3) 200-nautical mile (370km) line: Shows how far countries' agreed economic area extends beyond their coastline. Often set from outlying islands
4) Russian-claimed territory: The bid to claim a vast area is being closely watched by other countries. Some could follow suit  
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