Hundreds of people in kayaks and small boats have staged a protest in the north-western US port city of Seattle against oil drilling in the Arctic by the energy giant Shell.

Paddle in Seattle was held by activists who said the firm's drilling would damage the environment.

It comes after the first of Shell's two massive oil rigs arrived at the port.

The firm wants to move them in the coming months to explore for oil off Alaska's northern coast.

Earlier this week, Shell won conditional approval from the US Department of Interior for oil exploration in the Arctic.

The Anglo-Dutch company still must obtain permits from the federal government and the state of Alaska to begin drilling.

It says Arctic resources could be vital for supplying future energy needs.

'The only safe place'

The flotilla of kayaks, canoes, sailboats and paddle boats gathered near the 400ft (122m) tall Polar Pioneer drilling rig.

A solar-powered barge - The People's Platform - joined the protesters, who chanted slogans and also sang songs.

"This weekend is another opportunity for the people to demand that their voices be heard," Alli Harvey, Alaska representative for the Sierra Club's Our Wild America campaign, was quoted as saying by the Associated Press news agency.

"Science is as clear as day when it comes to drilling in the Arctic - the only safe place for these dirty fuels is in the ground.''

The protesters later gathered in formation and unveiled a big sign which read "Climate justice now".

They mostly stayed outside the official 100-yard (91m) buffer zone around the Polar Pioneer, the Seattle Times newspaper reports.

Police and coastguard monitored the flotilla, saying it was peaceful.

The demonstrators are now planning to hold a day of peaceful civil disobedience on Monday in an attempt to shut down Shell operations in the port, the newspaper adds.

The port's Terminal 5 has been at the centre of a stand-off between environmentalists and the city authorities after a decision earlier this year to allow Shell use the terminal as a home base for the company's vessels and oil rigs.

Shell stopped Arctic exploration more than two years ago after problems including an oil rig fire and safety failures.

The company has spent about $6bn (£3.85bn) on exploration in the Arctic - a region estimated to have about 20% of the world's undiscovered oil and gas.