The fourth floor of the store has been decked out with more than 50,000 Christmas decorations - with another 70,000 to come between now and December.
Selfridges, which also has branches in Manchester and Birmingham, imported many of the hand-made baubles from Hungary.
The store insists that with 145 shopping days left to Christmas, customers - especially from overseas - have already started their seasonal shop.
But not everyone is feeling the festive spirit, with Twitter user Trevor A Bishop tweeting: “This helps take all the magic, wonder and being special out of Christmas. Far too early. Only interested in their own profit.”
Bruce Summers tweeted: “Bloody hell most folk not even finished summer holidays yet!!”
Geraldine James, the firm’s Christmas decorations buyer, said: “We’ve been working on this year’s Christmas shop since Christmas last year.
“We have so many customers visiting us from all over the world and eager to snap up festive souvenirs on their summer holidays, which they can’t buy at home.”
She added: “We have been opening the doors to our Christmas Shop during the summer for years now and have become a real destination for those fans of Christmas and festive decorations within and outside the UK.”