According to reports, hundreds of thousands of Polish people, as well as Jews from a number of other European countries, had been held prisoner there in appalling conditions and many had been killed in the gas chambers.
Few details have emerged of the capture of Auschwitz, which has gained a reputation as the most notorious of the Nazi death camps.
Some reports say the German guards were given orders several days earlier to destroy the crematoria and gas chambers. Tens of thousands of prisoners - those who were able to walk - had been moved out of the prison and forced to march to other camps in Germany.
Details of what went on at the camp had been released previously by the Polish Government in exile in London and from prisoners who have escaped.
In July 1944 details were revealed of more than 400,000 Hungarian Jews who were sent to Poland many of whom ended up in Auschwitz. They were loaded onto trains and taken to the camp where many were put to death in the gas chambers.
Before they went they were told they were being exchanged in Poland for prisoners of war and made to write cheerful letters to relatives at home telling them what was happening.
According to the Polish Ministry of Information, the gas chambers were capable of killing 6,000 people a day.
Another report from Poland told of mass arrests in the village of Garbatka near Radom in the early hours of one morning in August 1942. Workmen were accused of plotting to blow up a local factory. Twenty were executed on the spot, the rest were sent to Auschwitz.
Since its establishment in 1940, only a handful of prisoners have escaped to tell of the full horror of the camp.
In October last year, a group of Polish prisoners mounted an attack on their German guards. The Germans reportedly machine-gunned the barracks killing 200 Polish prisoners. The Poles succeeded in killing six of their executioners.
When the Red Army arrived at the camp they found only a few thousand prisoners remaining. They had been too sick to leave.
The capture of Auschwitz came as the Red Army had made important advances on three fronts: in East Prussia to the north, in western Poland as well as Silesia in eastern Germany. Fighting continued around the historic Polish western city of Poznan.
The Polish capital, Warsaw, was liberated a week before after five-and-a-half years of German occupation.
Although few details of the liberation of Auschwitz were given in the British press at the time, it had gained a reputation as the worst of the German concentration camps.
On 8 May 1945 a State commission compiled by the Soviets with advice from Polish, French and Czechoslovak experts revealed the full horror of conditions at the camp.
Nearly 3,000 survivors of various nationalities were questioned and on the basis of their evidence the report estimated 4,000,000 people had perished there between 1941 and early 1945.
The dead included citizens from the Soviet Union, Poland, France, Belgium, Holland, Czechoslovakia, Yugoslavia, Hungary, Italy and Greece.
The commission, which had previously investigated conditions at Majdanek, Treblinka and other camps, described Auschwitz as the worst in its experience.
It found evidence of experiments carried out on humans "of a revolting character".
According to the evidence, the commission said the Germans had moved out up to 60,000 inmates - those still fit enough to walk - when they retreated. The few thousand who were left behind were freed by the Russians.
They also found seven tons of women's hair, human teeth, from which gold fillings had been extracted and tens of thousands of children's outfits.
The final death toll was later revised downwards, by the Auschwitz Museum, to between 1 and 1.5 million, including almost 1m Jews.
To hear audio recollections by survivor Leon Greenman being deported to the camp, click on the link below: (First broadcast by the BBC 27 January 1995).