Canadian director James Cameron, best known for churning out box office hits, can now add another accomplishment to his long resume -- reaching the Earth's deepest point, alone.

The director of "Titanic" and "Avatar" descended nearly 11 kilometres below the Pacific Ocean's surface Sunday afternoon in a specially designed submarine called the Deepsea Challenger. He returned to the ocean's surface Sunday night.

Cameron is only the third man in history to complete the dive into the ocean's deepest valley, Mariana Trench -- and the first to do so alone. He touched down at the trench's deepest and darkest point, called Challenger Deep.

Mariana Trench is located about 320 kilometres southwest of the island of Guam.

"Just arrived at the ocean's deepest pt. Hitting bottom never felt so good. Can't wait to share what I'm seeing w/ you," read a message posted on Cameron's Twitter account just before 6 p.m. Eastern Time on Sunday.

In an earlier tweet, Cameron said his deep-sea voyage was the culmination of seven years of work and preparation.

As an explorer-in-residence with the National Geographic Society, Cameron was planning to spend several hours trekking across Mariana Trench, collecting data and specimens and, of course, filming the entire experience.

The massive trench is 120 times larger than the Grand Canyon and dangerous to explore because of extreme water pressure at such depths. Little is known about the species and plants that survive there.

Swiss engineer Jacques Piccard and U.S. Navy captain Don Walsh were the only other explorers who managed to reach Mariana Trench during a 1960 dive. But they spent only 20 minutes at the bottom after their submarine kicked up sand from the sea floor, reducing their visibility.

Cameron has been practicing deep sea diving off Papua New Guinea to prepare for the challenge. He has described the Deepsea Challenger submarine as a "vertical torpedo," engineered to sink upright and spinning -- "like a bullet fired straight into the Mariana Trench," according to a National Geographic report.

The submarine's pressure-resistant shape and custom-designed foam filling prevented it from buckling under water pressure equalling about eight tons per square inch.

Cameron has made 72 deep-sea dives over the years, many of them to explore the Titanic wreckage in preparation for his 1997 hit movie.

With files from The Associated Press