A letter in which Albert Einstein shared his thoughts on God and the Bible has sold at auction for $2.9m.

Christie's had expected the handwritten letter to fetch $1.5m when it went under the hammer at its New York City auction room on Tuesday.

The letter is one-and-a-half pages long and was written by the famous scientist in German to the philosopher Eric Gutkind in 1954, the year before Einstein's death.

In the letter, Einstein shared with Gutkind that he did not regard the Bible as anything more than a collection of 'legends' and that even his own Jewish faith was 'superstition'.

'The word God is for me nothing but the expression and product of human weaknesses,' he wrote, 'the Bible a collection of venerable but still rather primitive legends.'

He continued: 'No interpretation, no matter how subtle, can [for me] change anything about this.'

Regarding the Jewish faith, he wrote that it was in his view 'like all other religions, an incarnation of primitive superstition'.

'The Jewish people to whom I gladly belong, and in whose mentality I feel profoundly anchored, still for me does not have any different kind of dignity from all other peoples.' he said.

A Bible up for auction at Sotheby's last week shed more light on Einstein's views on the Christian faith.

It was given by Einstein to an employee in 1932 and contained a brief inscription on the inside from the scientist.

'This book is an inexhaustible source of living wisdom and consolation,' he wrote.

It had been expected to fetch $300,000 at Sotheby's New York City auction room last week but it failed to find a bidder.