"People were running down but didn't know where to go, so a lot of people were lost on the mountain on the wrong side, wrong route and then you have a big problem," Mr van Rooijen told Reuters news agency from his hospital bed.
He said he was screaming for people to work together, but many of them failed to react, apparently locked in their own personal struggle to survive.
Among the 11 listed as dead is Gerard McDonnell, from Ireland.
Friend Pat Falvey said the climber's family "are holding up well and are very proud of Ger's achievement and are still in total shock in relation to the fact that he may not be coming back".
He said they did not expect to retrieve Mr McDonnell's body from such a high altitude.
K2 lies near Pakistan's northern border with China. It is regarded by mountaineers as more challenging to conquer than Mount Everest, the world's highest peak.
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