On the deepest ocean dive ever made by a human inside a submarine, a Texas investor and explorer found something he could have found in the gutter of nearly any street in the world: trash.

Victor Vescovo, a retired naval officer, said he made the unsettling discovery as he descended nearly 10,928 metres (more than 10 kilometres) to a point in the Pacific Ocean's Mariana Trench — the deepest place on Earth.

His dive took him 16 metres lower than the previous deepest descent in the trench in 1960.

Vescovo found undiscovered species as he visited places no human had gone before.

Sea creatures swim around part of a submersible lander, illuminated by the light of the submarine DSV Limiting Factor on the floor of the Mariana Trench, in a still image from video released by the Discovery Channel. (Discovery Channel/Reuters )

On one occasion, he spent four hours on the trench floor, viewing sea life ranging from shrimp-like arthropods with long legs and antennae, to translucent sea pigs, which are similar to sea cucumbers.

He also saw angular metal or plastic objects — one with writing on it.

"It was very disappointing to see obvious human contamination of the deepest point in the ocean," Vescovo said.

Plastic waste has reached epidemic proportions in the world's oceans, with an estimated 100 million tonnes dumped there to date, according to the United Nations.

Scientists have found large amounts of microplastic in the guts of deep-dwelling ocean mammals like whales.

Third time to Challenger Deep

Vescovo hopes his discovery of trash in the Mariana Trench will raise awareness of how much is dumped in the oceans, and will pressure governments to better enforce existing regulations, or put new ones in place.

"It's not a big garbage-collection pool, even though it's treated as such," Vescovo said of the world's oceans.

In the last three weeks, the expedition has made four dives in the Mariana Trench in Vescovo's submarine, DSV Limiting Factor, collecting biological and rock samples.

A technician checks the DSV Limiting Factor aboard the research vessel DSSV Pressure Drop above the Mariana Trench in an undated photo released by the Discovery Channel. (Atlantic Productions for Discovery Channel/Tamara Stubbs/Reuters)

It was the third time humans dived to the deepest point in the ocean, known as Challenger Deep.

Canadian filmmaker James Cameron was the last to visit the location in 2012 in his submarine, when he reached a depth of 10,908 metres.

Before Cameron's dive, the first-ever expedition to Challenger Deep was made in 1960 by the U.S. Navy, which reached a depth of 10,912 metres.