Traffic on a pivotal subway line in Shanghai has resumed, five hours after its closure for systems failure and subsequent collision of two trains.

A short circuit caused the line's power outage at about 6 a.m., halting traffic between Southern Shaanxi Road and People's Square, in the city center. As the power system was about to be restored, two subway trains collided at 7 a.m.. No injuries were reported.

The collision led to the complete shut-down of Line 1, forcing thousands of passengers to take buses. City public transport operators, mobilized 80 additional buses to divert the crowds during the morning rush hour. The Shanghai Metro has published an apology on its official Web site. The cause of the accident is being investigated.