This NY Times report during the war is as explicit as anyone could expect, including descriptions of mass murders in gas chambers (a typo on the beginning year, should be: 1941) and a remarkable estimate of five & a half million Jews murdered so far.
The report from Hungary itself is somewhat inaccurate.
One million is roughly the total of pre-war Hungarian Jews, of whom around 250,000 survived the war.
Of the remainder, 440,000 are "now" being shipped to Auschwitz and of those 90% will be immediately gassed.
The fate of the remainder is not clear, but, for example, 42,000 Hungarian Jewish forced laborers died on the Russian front in 1942-43.
Where’s Soros?
Yet, somehow, no one knew until western allies actually went inside the camps with cameras a year from now.