An American diver who travelled to the deepest part of the Pacific ocean has alarmingly encountered floating plastic trash on the deepest known reaches of the ocean floor.

The disheartening discovery was made by Victor Vescovo during a four-hour underwater excursion where he descended some 11km in the Pacific Ocean’s Mariana Trench, breaking the record for deepest ever submarine dive.

There, in one of the deepest reaches of the underwater world, the team discovered a plastic bag and lolly wrappers drifting between the stunning array of new sea creatures that he spotted.

On a more heartening note, the submariners said they came across four new prawn-like species called amphipods and brightly coloured rocky outcrops, possibly created by microbes on the seabed.

Unsurprisingly, they also stumbled across other known inhabitants of the deep sea, including a spoon worm 7,000 metres-down and a pink snailfish 8,000 metres-down.

Among the pollution, the diving team believe they have uncovered four new prawn-like species. Photo: Atlantic Productions Discovery Channel 

The scientists took back with them some deep sea creatures for testing to see if they had ingested microplastics.

The ocean is filled each year with about 8 million metric tons of plastics, but not much is known about where the pollution actually ends up.

The team plunged down into the Mariana Trench five times as part of Mr Vescovo’s so-called “Five Deeps expedition,” to explore the deepest parts of all five oceans.

Mr Vescovo travelled exactly 10,927 metres beneath the ocean, making it the third time any human has ever reached such extreme depths.

“It is almost indescribable how excited all of us are about achieving what we just did,” Mr Vescovo told the BBC.

“This submarine and its mother ship, along with its extraordinarily talented expedition team, took marine technology to a ridiculously higher new level by diving – rapidly and repeatedly – into the deepest, harshest, area of the ocean.”

Vescovo broke the previous Mariana Trench diving record. Photo: Atlantic Productions Discovery Channel 

US Navy lieutenant Don Walsh and Swiss engineer Jacques Piccard were the first people to journey down to the bottom, after taking their steel submarine as far down into the deep abyss as possible before making the dive. The pair accomplished the record-breaking dive on January 23, 1960.

Half a century later, filmmaker James Cameron made a 70-minute record-breaking solo ascent in March of 2012 in his bright green submarine.

Mr Walsh watched the team dive to the bottom of the ocean. 

“I salute Victor Vescovo and his outstanding team for the successful completion of their historic explorations into the Mariana Trench,” he told the BBC.

“Six decades ago, Jacques Piccard and I were the first to visit that deepest place in the world’s oceans.

“Now in the winter of my life, it was a great honour to be invited on this expedition to a place of my youth.”