Network Rail has released images showing the work taking place at London Bridge.
Up to and including September 2, Southeastern trains that would usually run into London Bridge, Charing Cross and Waterloo East have been diverted to Cannon Street, Blackfriars, Victoria and Waterloo to a wholly revised timetable.
NR said great progress has already been made with new track and signalling equipment installed, which it said allowed the lines to reopen in the early hours of Monday morning as planned.
Focus has now shifted to the Charing Cross lines, where engineers have completely replaced three tracks into London Bridge and reorganised the layout so that from September 3, Charing Cross trains will be able to run through the brand-new Bermondsey Dive Under railway junction. Work will continue at London Bridge and near New Cross until very early on Sunday morning when Network Rail will open the new platform 6 at London Bridge, allowing more Charing Cross trains to stop at the station.