The Mayor of London Boris Johnson gave the signal to start major works yesterday, 23 November.
Approximately 600,000 tonnes of earth will now be excavated from beneath South London to develop the extension.
A 300m long conveyor belt will transport spoil to the banks of the River Thames as part of the project.
The Ferrovial/Agroman/Laing O'Rourke JV, which was awarded the £500m main works and design contract in 2014, will develop two new 3.2km tunnels.
In addition, two new stations will be built; one at the Battersea Power Station redevelopment and another at Nine Elms.
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Waste created by by the project will be transported to a farm in Essex to be used for arable farmland.
Tunnelling works on the extension are to due to begin in early 2017 and will take six months to complete.
The Mayor of London, Boris Johnson, said: "The whirring into action of this fantastic machine marks a key moment in the delivery of the Northern line extension. This gigantic conveyor belt will enable a staggering 600,000 tonnes of material to be excavated from beneath south London and transported safely by barge on the Thames.
"Once built, the extension of the Northern line will act as a major spur to regeneration and growth in the area. It will open up the Tube to thousands more Londoners, cut journey times and act as a catalyst for the creation of much-needed new homes and jobs."
Nick Brown, Managing Director, London Underground, added: "The extension of the Northern line is key to supporting and enabling homes, jobs and economic growth in this area.
"This extension, alongside our work to modernise the Tube network, will help us keep pace with the city's sharply rising population, and will create jobs through the supply chain across the UK."
(LM/MH)
