A floating device sent to corral a swirling island of rubbish between California and Hawaii has not swept up any plastic waste, but the young innovator behind the project says that a fix is in the works.

Boyan Slat, 24, who launched the Pacific Ocean clean-up project, said the speed of the solar-powered barrier was not allowing it to hold on to the plastic it had been catching.

Photo: The Pacific Ocean clean-up project aims to reduce the 1.8 trillion pieces of plastic swirling around. (AP: Lorin Eleni Gill)

"Sometimes the system actually moves slightly slower than the plastic, which of course you don't want because then you have a chance of losing the plastic again," Mr Slat said in an interview with The Associated Press.

A crew of engineers will work on the U-shaped boom for the next few weeks to widen its span so that it catches more wind and waves to help it go faster.

A ship towed the 600-metre-long barrier in September from San Francisco to the Great Pacific Garbage Patch — an island of trash twice the size of Texas.

It has been in place since the end of October, Mr Slat said.

The plastic barrier with a tapered 3-metre-deep screen is intended to act like a coastline, trapping some of the 1.8 trillion pieces of plastic that scientists estimate are swirling in the patch, while allowing marine life to safely swim beneath it.

Photo: Mr Slat said his organisation hopes to remove 50 per cent of the Great Pacific Garbage Patch in five years. (AP: Peter Dejong, file photo)

Mr Slat said he was not deterred by the setback because engineers expected to make tweaks to the system.

"What we're trying to do has never been done before," he said.

"So, of course we were expecting to still need to fix a few things before it becomes fully operational."

Fitted with solar-powered lights, cameras, sensors and satellite antennas, the device intends to communicate its position at all times, allowing a support vessel to fish out the collected plastic every few months and transport it to dry land for recycling.

Mr Slat said he expected shipping containers filled with fishing nets, plastic bottles, laundry baskets and other plastic trash scooped up by the system to be back on land within a year.

"We've given ourselves a year after launch to get this thing working," he said.

Project still faces scepticism

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The U-shaped barrier is designed to trap plastic on the surface while allowing marine life to swim safely beneath it. (ABC News)

Among those sceptical of Mr Slat's Ocean Cleanup project is George Leonard, chief scientist of the Ocean Conservancy, a non-profit environmental advocacy group.

Mr Leonard said that even if plastic trash could be taken out of the ocean, a lot more would continue pouring in each year.

He said any solution must include a multipronged approach, including stopping plastic from reaching the ocean and educating people to reduce consumption of single-use plastic containers and bottles.

Mr Slat agreed that preventing more plastic from entering the ocean was part of the solution but said something needed to be done about what was already there.

"This plastic doesn't go away by itself, and to just let hundreds of thousands of tons of plastic be out there to be fragmented into these small and dangerous microplastics to me seems like an unacceptable scenario," he said.