UPDATE: Shell's icebreaker ship, which had started heading towards the activists, has now turned back to the dock.
Suspended gracefully from the steel suspension bridge which crosses the Willamette River in Portland, with red and yellow flags billowing in the breeze, the figures resemble trapeze artists putting on a show for the world.
But the individuals camped out under St John's Bridge in Oregon are Greenpeace activists, attempting to block Shell's ship which is headed to the Arctic to drill for oil.
The 380ft Fennica was due to depart at 4.45am on Wednesday, but has yet to leave the port, the Guardian reports.
The 13-strong group of environmental activists, along with numerous kayakers, have spent the night dangling from Portland's tallest bridge bridge since 2am PT, in a bid to halt the ship's journey.
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"Every second we stop Shell counts," says Annie Leonard, executive director of Greenpeace US. "The brave climbers here in Portland are now what stand between Shell and Arctic oil. This is President Obama’s last chance to wake up and realise the disaster that could happen on his watch."
In May, Obama approved Shell's plan to drill for oil in the Chukchi Sea, in the Alaskan Arctic. According to Greenpeace, the Obama administration has predicted a 75% chance of a major oil spill if Shell develops its leases in the Sea.
Greenpeace activist Georgia Hirsty, one of the climbers rappelled from the bridge, said: "I'm filled with gratitude and humility for all those who have carried this fight."
Drilling at the oil company's Arctic site cannot proceed without the icebreaker ship, as it is carrying a key piece of safety equipment on board, which stops oil leaks if a well blows out.
A Shell spokeswoman added: "The Fennica will begin its return journey to Alaska once we’ve completed the final preparations."