'The Great Pacific Garbage Patch' is bigger than Britain and France combined - but one group is on a mission to start cleaning it up

The world's biggest ever ocean clean-up is underway.  

An experimental plastic-collection system is being towed out from California, in a bid to scoop the millions of tonnes of plastic waste floating in the Pacific ocean.

"If we don't do it now the plastic will break into smaller and smaller pieces. And the smaller the pieces are, the more harmful and the harder to extract from the marine environment," said Lonneke Holierhoek from The Ocean Clean-up.

The clean up will take place in the Eastern Pacific, called 'The Great Pacific Garbage Patch', which is bigger than Britain and France combined.

A giant tube 600 metres long will float on the surface and bend into a horse shoe shape, which will gather the plastic together in a small area.

Under the water a barrier will hang three metres down and trap plastic below the surface, designed so that any fish can pass under it.  

Once the plastic has been drawn into a dense mass, it will be collected by ship and taken away to be recycled.

But some experts worry the plastic trapping device could still harm marine life.

Sue Kinsey from Marine Conservation Society says the major problem is that there are creatures that passively float.

"They can't actually get out of the way and once they are in this array they are going to be trapped there and unable to move."

The plan is to eventually employ 60 of the collection devices.