Greenpeace said Monday its activists had arrived in the Arctic on board one of its ships to pressure Britain's Cairn Energy to stop oil operations off Greenland's fragile coast.

Cairn Energy is drilling two wells off the west coast of Greenland and plans to drill two more before the end of October, the watchdog said.

If the British group's prospecting is successful, the Arctic "could be flooded with oil companies, all trying to operate in hazardous polar conditions," Greenpeace said in a statement.

The region is home to blue whales, polar bears, seals and migratory birds.

According to Greenpeace, a Danish warship -- Greenland is part of Denmark -- was at the drilling site.

It had warned the captain of the Greenpeace ship, the Esperanza, that any violation of the 500-metre (0.3-mile) security zone around each drilling rig would result in his arrest.

"To be here and see a huge drilling rig in this beautiful and fragile environment is deeply shocking," said activist Leila Deen, who is onboard the Esperanza.

"This operation is too risky and companies like Cairn need to leave the Arctic alone and instead work quickly to develop safe and clean alternatives that will actually help us get off fossil fuels for good," she said.