Tube passengers face disruption after drivers walked out in a 24-hour strike at 21:00 GMT.
Rail and Maritime Transport (RMT) union members are protesting about the relocation of Tube drivers. Central, Waterloo and City lines are affected.
Maintenance workers on London Underground have separately voted to strike over a breakdown in relations. No date has been set for action.
Meanwhile, Southern Railway conductors are also set to walk out on Wednesday.
The dispute centres on a long-running row over the role of train guards.
Tube strike: What you need to know
Tuesday 21 February
- The walkout starts from 21:00 and Central line passengers must complete their journey by 23:30
- The Waterloo and City line is not expected to be affected
Wednesday 22 February
- No Waterloo & City services
- No Central line services east of Leytonstone
- From 05:30, no westbound Central line services between White City and Leytonstone
- From 07:00, very limited Central line services. Expect congestion and severe disruption
- The Central line closes at 23:00
Normal services are not expected to resume until Thursday.
Peter McNaught, operations director for the Central Line, said the Tube drivers' strike was "unnecessary".
He added: "We have made all reasonable efforts to resolve this dispute through talking."
Maintenance workers have voted to strike by two to one, and by nine to one for other forms of industrial action.
The RMT is now considering what form action should take.
General secretary Mick Cash said the "door has been slammed in our faces", despite "strenuous efforts" to resolve the dispute.
"If London Underground is allowed to get away with this move on the Central Line they will start shunting drivers around at the drop of a hat, regardless of the consequences," he added.
Southern said it hoped to run as many trains as possible during the strike on Wednesday.
During the previous conductors' strike on 23 January, about three-quarters of its regular service ran, the firm said.