A previously unsuspected sanctuary for polar bears in the arctic has been discovered, the makers of a British television documentary say.

An estimated 20 polar bears were seen on a large tabular iceberg in Baffin Bay, 30 miles off the Canadian coast, the filmmakers said.

Tabular icebergs, with steep sides and a flat top much like a plateau, could be giving the polar bears protection from being hunted on land, they said.

For most of the year, polar bears live on sea ice where they hunt seals.

It had been thought they had to move onto land during the summer months when sea ice melted, but the discovery of the bears on the iceberg suggests some spend those months surviving on large tabular icebergs off the coast.

"In recent years we've been seeing a lot more big tabular icebergs come off the Greenland ice sheet and they're now ending up in Baffin Bay," Keith Nicholls of the British Antarctic Survey, who was on the filming expedition, said.

Polar bears are hunted by humans on the mainlands of both Greenland and Canada and may have discovered safety on the icebergs, experts said.

"What's there for them is security, and I think they are taking advantage of that," Chris Packham of the BBC documentary crew said. "So I think they are living on this iceberg to stay safe, and just wait for the sea ice to come back in."