He bitterly recounted tales of climbers using vacant tents as toilets, stealing the provisions needed by other teams, and acting "like human lemmings" in their desire to reach Everest's 29,028-ft summit.
Mr Blessed, 59, said at a press conference in London that the mountain "stank of death". "Sixty per cent of the people out there hadn't a clue what they were doing. They had [climbing] permits like taffeta, but no preparation - they were turning up with one tent and no [bottled] oxygen, hoping other people would help them out."
He railed at what he saw as the despoilation of the mountain, first climbed in 1953, which now sees hundreds of attempts every year - often by inexperienced climbers who can afford the $65,000 (pounds 43,000) "peak fee". "The bodies were everywhere. An Austrian climber said to me, 'I don't accept that it's so dangerous up there'. I said, if you try to go up for four days without oxygen, in two days you will be a block of ice. And in two days he was."
He said that "summit fever" - the desire to reach the top - had overtaken some people's desire for self-preservation.
Mr Blessed also bemoaned plans for a hotel on the northern side of the mountain. "It will have the greatest view on God's earth, and then will come the funicular railways and then pressurised suits so that tourists can go to the top. In the days of Mallory and Irvine, in the 1920s, it used to be a magic place."
But Mr Blessed's perspective of mountaineering behaviour was questioned yesterday by Tom Prentice, editor of Climber magazine. "When Edward Whymper was making the first ascent of the Matterhorn in July 1865, he and his partners threw rocks from the summit at the two Italians who were competing for the first ascent . . ."
"I'm not condoning such behaviour, but I think Brian Blessed has an over- romantic view of mountaineering. said Mr Prentice. "The rubbish that gets left behind, the stealing of things - these are just a reflection of some of the problems that happen everywhere in society when you get a lot of people together. That's especially true in high-altitude mountaineering, which is stressful, both mentally and physically."
Mr Blessed, a climber with 30 years' experience, was making his third attempt to climb the mountain without oxygen. In 1993 he was forced to turn back at 28,200ft. This time he was sent back by the expedition leader at 25,200ft when the weather worsened. "You have to obey the rules of the mountain," he said.
His expedition was being filmed by ITN for a Channel 4 programme to be shown later this year. The British climbers Alan Hinkes and Matt Dickinson, who was also filming the climb, did reach the top.
Mr Prentice said: "I think that for Brian Blessed to complain about tourists is absurd. It's people like him going there and making television programmes, generating publicity, who keep Everest in the forefront of people's minds when they think about mountains."
Mr Blessed claimed that this would be "the last pure film" about Everest, and that any future expedition would find the mountain ruined by visitors.