Transport plans for London’s Olympics face their sternest test ahead of what is expected to be the Olympic Park’s busiest day since the Games opened.
More than 200,000 people will be at the park later, including up to 80,000 who will descend on the Olympic Stadium for the start of athletics events.
The Central Line, which serves the Olympic Park in Stratford, is suspended from Liverpool Street to Leytonstone.
British hopes for medals are in rowing, track cycling and swimming later.
Problems on the Central Line follows a signal failure at Bethnal Green station, London Underground said. Tickets are being accepted on National Rail services in the area, while Transport for London are encouraging those attending the Games to use alternative lines and stations close to the Olympic Park.
Team GB have risen to fifth in the overall medal table with five golds after three were secured on Thursday.
Among the gold medallists on day six were track cyclist Sir Chris Hoy. His victory, with Philip Hindes and Jason Kenny in the team sprint, represented his fifth Olympic title and equalled rower Sir Steve Redgrave’s record British,
Meanwhile, hopes are high for rowers Katherine Grainger, who has three silvers from three previous Olympics, and Anna Watkins in the double sculls, swimmer Rebecca Adlington, who defends her 800m freestyle title, and the men’s track cycling pursuit team.
Highly fancied heptathlete Jessica Ennis also gets her campaign under way at the Olympic Stadium, in the 100m hurdles, the high jump, the shot put and the 200m.
Other British athletes in action on Friday will include world champion Dai Greene in the men’s 400m hurdles heats and defending Olympic champion Christine Ohuruogu in the women’s 400m.
In developments on Thursday:
* Peter Wilson took gold for Britain in the men’s double trap shooting event. He said it “felt amazing” and was “a dream come true”
* Etienne Stott and Tim Baillie triumphed in the two-man canoe slalom at at the Lee Valley White Water Centre, ahead of fellow Britons David Florence and Richard Hounslow
* US swimmer Michael Phelps won his 20th Olympic medal, in the men’s 200m individual medley and became the first swimmer to successfully defend the same title twice. He will be looking to win his 21st Olympic medal on Friday when he takes part in the men’s 100m butterfly
* The latest set of Royal Mail stamps honouring Britain’s gold medallists were printed in the wake of Thursday’s three golds, with the promise of more to come with each gold medal
* Sports Minister Hugh Robertson said Team GB’s “superb performances” had given them great momentum
Friday’s events at the 80,000-capacity Olympic stadium will bring thousands more people pouring into the east London park and mean access to the neighbouring Westfield shopping centre will be restricted for the next two days.
Only staff and Olympic ticket holders will be able to go into the centre between 10:30 BST and 17:00 as organisers seek to minimise congestion.
Transport for London (TFL) said public transport services and roads to the Olympic Park would be exceptionally busy on Friday and urged anyone not going to the site to avoid the area.
The Docklands Light Railway, Jubilee and Central lines are expected to be busier than usual, especially in the morning, evening and late-evening peaks and driving in central London should be avoided where possible, TFL said.
London’s transport commissioner Peter Hendy said: “This Friday and Saturday will be the busiest days of the Games so far as the Olympic Stadium opens its doors and sporting events continue to take place across the capital.
“Westfield Stratford City may not be open to shoppers without a ticket during these times but London has a rich and vast array of other attractions to offer during the Games.”
Among other British sporting interest on Friday will be Andy Murray playing Novak Djokovic in the men’s tennis singles semi-finals at Wimbledon, and Great Britain’s women’s football team taking on Canada in their quarter-final match in Coventry.