Tube trains to the Olympic Park were suspended this morning.
Spectators travelling to Stratford on the Central line at around 7am were told all services were terminating at Liverpool Street due to an incident at Leyton.
As Simon Harris reports, a train was taken out of service after the driver reported smelling smoke:
Services were suspended from 7am for three hours between Liverpool Street and Woodford, leaving passengers stranded at Bethnal Green, Mile End and Stratford.
Travellers on the Tube were advised to avoid the Central Line and take the District or Jubilee lines to Stratford instead.
To add to the Olympic travel problems, rail services in and out of Liverpool Street main line station were disrupted due to an overhead wire problem between Elsenham and Stansted Mountfitchet in Essex.
The problems around Liverpool Street come on another busy day for public transport as the first weekday evening football match takes place at Wembley Stadium.
This is only one of a number of Olympic events taking place in the capital, with Transport for London (TfL) advising that London is expected to be exceptionally busy throughout the day.
TfL says people are heeding advice to avoid London if possible.
It says that while Tube journeys were up 4% yesterday, road journeys in London were down by 20%.
Meanwhile, the RMT transport union has called for an immediate investigation into "the real impact of cuts to fleet maintenance schedules" following the incident.
The union said it was emerging that the likely cause of today's problem was defective brakes.