Most London Underground services remain suspended as a walkout by staff continues for a fourth day.
Members of the Rail, Maritime and Transport union (RMT) are carrying out a “rolling strike” in a dispute over pay and its unmet demand for a 32-hour working week.
A handful of Tube stations appear to be open on the ends of the Northern, Central, Metropolitan and District lines but most routes through central London are closed.
The Docklands Light Railway (DLR) is suspended as part of a separate dispute. The Elizabeth and Overground lines remain open.
Transport for London (TfL), which offered staff a 3.4% pay rise, said the demands for a shorter working week were unaffordable, with a 32-hour week costing the network around £200m.
The RMT said it did not expect an 32-hour week immediately, but a gradual reduction.
Asked on BBC Radio 4’s Today programme whether the strikes would continue, Eddie Dempsey, general secretary of the RMT, said: “They [TfL] may want the strikes to carry on.
“So where we’ve got to is we’re coming towards the end of a week of running strike action. We’re open to negotiations – as we always are – but as it stands, there are no invitations for us to sit down and negotiate with TfL.”
Nick Dent, TfL director of customer operations and head of the negotiation team, said: “We are very keen to work with the RMT.
“The first thing we have asked them to do is put this offer to their members, they launched their ballot before we’d made any pay offer, so members were voting without understanding what the pay offer actually was.”
Depot managers and signallers from the RMT are among those withdrawing their labour.
Londoners have used a combination of boats, bikes and buses to get around the capital, with a large spike in bike rental schemes.
The prime minister and the mayor of London are among those calling for both sides to negotiate after talks broke down last Wednesday morning.
On Tuesday, Mr Dempsey criticised Sadiq Khan, blaming him for a “total and utter collapse of industrial relations in London”.