London's underground train network was to grind to a virtual halt for several days late Sunday due to a strike over wages.
Transport for London, which runs the "Tube," said "little or no" services were expected between Sunday evening and Friday morning in the British capital.
The transport authority warned users to complete their journeys by 5:30 pm (1730 GMT).
A return to normal service is not expected until midday on Friday, it added.
Some 10,000 members of the Rail, Maritime and Transport union (RMT) were due to walkout amid a dispute over a five percent pay offer.
"Transport for London has failed to avert this strike by not offering a deal that was acceptable to our members on London Underground," an RMT spokesperson said.
"We do not take strike action lightly but we are determined to get a negotiated settlement on pay, travel facilities and a grading structure that means our members will not lose out."
The industrial action has been mirrored across the public and private sectors in Britain, as workers demand pay rises in response to decades-high inflation and the worst cost-of-living crisis in a generation.
Those who have taken to picket lines over the last 18 months have ranged from health sector employees and teachers to lawyers and dock workers.
Junior doctors are due to end their longest consecutive strike in the seven-decade history of Britain's National Health Service (NHS) on Tuesday.
