Australia's majestic coastlines and the world's oceans are in grave danger of becoming a "toxic plastic soup", a leading conservation body has warned.

An ever-increasing quantity and density of deadly plastic is forming along the Australian coast, killing seabirds, marine animals and posing unknown risks to humans.

WARNING: Graphic images in this story could disturb some readers.

Foundation for National Parks and Wildlife (FNPW) chief executive Ian Darbyshire told Nine.com.au the most disturbing part of the problem is that it is rapidly accelerating at an alarming rate, out of sight of most people.

"The ocean has always been the hardest place to get people to care about," Darbyshire said.

Dr Jennifer Lavers of University of Tasmania cuts open dead seabirds on Australia's Lord Howe Island, finding each animal's stomach full of deadly plastic. (United Nations)

"For some reason, mankind has always treated the ocean that it is a huge and somewhat scary place. It's always been seen as a good place for people to dump rubbish and to take marine life from, and that it will just continue ad infinitum."

In Australian waters, FNPW data shows floating plastic debris ranges from a few thousand pieces per square km to more than 40,000 pieces per square km.

Disturbing footage from a recent United Nations film showed a University of Tasmania researcher cutting open dead seabirds on Australia's Lord Howe Island, a world heritage site, and finding their stomachs rammed full of plastic.

The worst case Dr Jennifer Lavers found was a 90-day-old chick that had fatally ingested 276 pieces of plastic.

According to UNESCO, plastic debris kills more than 1 million seabirds every year, as well as more than 100,000 marine mammals.

According to UNESCO, plastic debris kills more than 1 million seabirds every year, as well as more than 100,000 marine mammals.

Up to 12.7 million tonnes of plastic waste is washed into the ocean each year, according to 2015 research in the journal Science ; that equates to one garbage truck a minute.

Australians are estimated to use more than 6 billion single-use plastic bags every year. Currently, NSW is the only Australian state not to have a plastic bag ban implemented or pending.

A NSW Environment Minister spokeswoman did not say why NSW appeared to be out of step with other state governments.

In NSW, Coles, Woolworths and Harris Farm Markets last year committed to voluntarily stop giving free plastic bags to customers.

Bottlenose dolphin swimming in an oil slick, with a black plastic bag along its belly, in Curacao, Netherlands Antilles. (GETTY)

The spokesperson said the Gladys Berejiklian-led government "commends the proactive step of retailers".

She added NSW's recently-launched container deposit scheme showed over 117 million drink containers have been returned across the state.

But critics have argued NSW government needs to outright ban plastic bans. FNPW boss Darbyshire said Australians needed to urgently modify their behaviour, and pinpointed littering on beaches, rivers and dried creek beds as a major contributor to the problem.

"We are heading very quickly to the point where there will be more plastic in the ocean than there are animals," Darbyshire said.

Graphic from 2015 UNESCO report illustrating the rise of global plastic production. (UNESCO)

"The Pacific Ocean has now got a floating island plastic that I'm told is twice the size of Texas."

Darbyshire said the dangers are now hidden and go beyond the shocking and tangible images of turtles and birds caught and trapped by plastic rubbish.

Scientists have determined plastic in the ocean breaks down into microbe particles.

Sea plants and plankton eat these tiny toxic pieces and the poisons filter all the way up the food chain on to dinner plates across the world.

"This has longer-term, unknown concerns," Darbyshire said.

Up to 12.7 million tonnes of plastic waste is washed into the ocean each year, according to 2015 research.

Conservationist Sir David Attenborough said he and his crew were shocked by what they found, even in the most remote ocean locations, while filming Blue Planet II .

The veteran British broadcaster said the tremendous scale of the problem was now putting the future of humanity at risk.

Attenborough said rising ocean temperatures and plastic in the world's seas requires immediate international action.

"We could actually do something about plastic right now. And I just wish we would," Attenborough said.

"There are so many [ Blue Planet II filming] sequences that every single one of us have been involved in … where we have seen tragedies happen because of the plastic in the ocean.

Sir David Attenborough speaking to the media as he arrives for the World Premiere screening of the BBC's Blue Planet II at the British Film Institute IMAX cinema in London. (AAP)

"We've seen albatross' come back with their belly full of food for their young and nothing in it.

"The albatross parent has been away for three weeks gathering stuff for her young and what comes out? What does she give her chick?