A Norwegian spruce, which is sent to London every year for Christmas, has been felled in a traditional ceremony.
To make the tradition more environmentally friendly, this year the tree is travelling to the capital by electric truck and a new tree has been planted in Oslo, to replace it.
A tree is sent from Norway each year as token of thanks for Britain's support during World War Two.
Once in the capital, the 56-year-old, 20m high tree will be erected in Trafalgar Square.
Organisers described the spruce as "one of the world's most famous Christmas trees" representing "friendship between cities and countries, peace, and solidarity."
It will be decorated with energy-efficient lightbulbs, hanging vertically in traditional Norwegian fashion.
The British ambassador to Norway, Jan Thompson, said: "It isn’t Christmas in the UK until the Trafalgar Square tree arrives."
She added that the tree had "brought joy to generations of Londoners", and said: "For many people visiting London it is as essential to see the Norwegian tree as to go Christmas shopping in Oxford Street or catch a show in the West End."
Oslo's mayor Anne Lindboe said the tree's meaning - of gratitude, friendship, and peace - was "just as significant today as it was 77 years ago."
The Lord Mayor of Westminster, Robert Rigby, thanked Norway for the tree and said: "They have done a tremendous job as ever - it looks majestic."
The tree lights will be switched on on 5 December.