London's Olympic transport system faced a major test on Friday as thousands headed for the Olympic Park for one of the busiest days of the games so far – as track and field events kicked off at the main stadium.

Severe delays were reported on several routes to the park on Friday.

Transport for London reported that the underground's Central Line, which links the center of the city with the Olympic complex, had been briefly suspended because of a signal failure.

The delays have a knock-on effect throughout the system as commuters and Olympics fans switch to other lines.

Officials were also restricting access to an oversize shopping mall next to the Olympic Park on Friday and Saturday because of the large crowds expected.

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Source: AP

Editor: Huan CAO

Voiceover: Chris Clark

Producer: Flora Yue