Construction has started on the £1bn extension of the London Underground (LU's) Northern Line from Kennington to Battersea via Nine Elms in the UK.

In last August, the Ferrovial Agroman Laing O'Rourke joint venture was awarded the £500m main works design and build contract by Transport for London (TfL).

Works will see the excavation of around 600,000t of earth from beneath south London to build the Northern line extension.

The extension will see construction of two new 3.2km tunnels and two new stations at Nine Elms and Battersea. It is expected to support around 25,000 new jobs.

"The extension of the Northern line will act as a major spur to regeneration and growth in the area."

Mayor Boris Johnson has given a signal to start a specially designed 300m-long conveyor belt that will transport soil to the banks of the River Thames.

Tunnelling work is scheduled to start in early 2017 and will take six months to complete, while the project is expected to be completed in 2020.

The £1bn project is being funded entirely through developer contributions from Battersea Power Station and other developers.

Following completion, the project will reduce journey times to the West End and the city to less than 15min.

Johnson said: "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.

"It is one of a number of major ongoing investments we're making into improving London's transport infrastructure, which will be ever more important as our city continues to grow."

In March, France-based NFM Technologies was contracted by London Underground (LU) to design, manufacture and deliver two tunnel boring machines (TBM) to build the Northern line extension.

The TBMs will measure 106m in length, and their cutting head will be slightly more than 6m in diameter.

In February, the European Investment Bank (EIB) has agreed to provide a £480m loan for the project.

Image: The extension will have two new stations at Nine Elms and Battersea. Photo: courtesy of Transport for London.