Michael Knight, president of the Sydney Organizing Committee for the Olympic Games, on Wednesday said he could not rule out major accidents on Sydney's rail network during the Games, as investigations began into a fire and a collision on Sydney's disaster-prone rail network Tuesday night.

"Nobody can guarantee that during the Olympic period there won't be a derailment, there won't be a breakdown, there won't be a repetition of one of the unfortunate incidents . . . like occurred last night," the SOCOG chief told reporters at the Japan National Press Club in Tokyo.

Six people were injured and up to 80 others were forced to evacuate a train after a suspected electrical fault sparked a fire in a carriage in the Blue Mountains west of Sydney on Tuesday night.