James Cameron, director of such Hollywood smashes as Titanic and Avatar, descends to the Mariana Trench in the Pacific National Geographic

The film director James Cameron was today described as a real-life Avatar after he returned safely from a one-man mission to the Mariana Trench, the deepest point of Earth's oceans.

Cameron emerged from his 12-tonne, lime green submarine, Deepsea Challenger, early this morning after travelling nearly seven miles down to the desert-like bottom of the trench. His ship was equipped with 3D cameras to shoot footage for a planned documentary, using lighting from a spectacular eight-foot tower of LEDs. The director of Titanic and Avatar, who has maintained a long-term interest in the secrets of the oceans' depths, was able to direct and film the action from within the sub.

"There is scientific value in getting stereo images because ... you can determine the scale and distance of objects from stereo pairs that you can't from 2D images," Cameron told National Geographic News ahead of the dive. As he reached the bottom of the trench, which is about 200 miles south-west of the Pacific island of Guam, Cameron sent out a tweet reading: "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".

James Cameron's Deepsea Challenger submersible. Photograph: Reuters

The Mariana is 120 times larger than the Grand Canyon and more than a mile deeper than Mount Everest is tall. The dive was the first into the depths of the trench since Swiss engineer Jacques Piccard and US navy captain Don Walsh spent 20 minutes there in 1960. Unlike Cameron, they were unable to see – let alone film – very much as their submarine kicked up too much mud from the ocean floor.

Expedition doctor Joe MacInnis said Cameron's journey had been "the ultimate test of a man and his machine", describing his friend as a real-life "avatar". He said: "He's down there on behalf of everybody else on this planet. There are seven billion people who can't go, and he can. And he's aware of that."

The expedition was organised and funded by Cameron himself, an oceanography enthusiast since childhood, along with the National Geographic Society, Rolex and Microsoft co-founder Paul Allen. The director, 57, has undertaken 72 deep-sea submersible dives, 33 of which were to the wreckage of the Titanic, the subject of his 1997 hit film. He expects the trip to the Mariana Trench to be the first of many.

Expedition member Patricia Fryer told National Geographic News the Deepsea Challenger's journey to the depths was far more useful scientifically than cheaper unmanned missions. "The critical thing is to be able to take the human mind down into that environment," said the marine geologist. "To be able to turn your head and look around to see what the relationships are between organisms in a community and to see how they're behaving – to turn off all the lights and just sit there and watch and not frighten the animals, so that they behave normally. That is almost impossible to do with an ROV [remotely operated vehicle]."