London Underground block closures begin
Tube passengers have been told to expect delays as sections of the Circle and District lines have been closed for four weeks for upgrade work.
Both lines will remain suspended between High Street Kensington and Edgware Road until 23 August.
London Underground (LU) said the work was to improve service reliability and to renew old infrastructure on one of the oldest sections of the Tube.
Work to prepare for new longer trains will also be carried out.
It will include track and drainage renewal and power upgrades to support the trains coming into service.
The seven-carriage air-conditioned trains - which will have room for an additional 143 passengers per train - which will start operating on the Hammersmith & City and Circle lines from the end of 2012.
LU said the block closure would allow the work to be done at a time when about 25,000 fewer passenger a day use that section of the Tube.
Completing the work using weekend track closures alone would result in a least 20 closures across six months or more, it said.
David Waboso, from LU, said: "We are determined to carry out this work in a way that keeps disruption to passengers to an absolute minimum.
"But we do hope any disruption caused by this block closure will be significantly outweighed by the huge overall benefits of this essential improvement work."