A track fault is likely to blame for the train derailment and crash near Paris on Friday that left six people dead and nearly 200 injured, nine of them in critical condition.
The commuter train, packed with 385 passengers, careened off the rails and crashed into a station platform at Bretigny-sur-Orge shortly after leaving the French capital during rush hour. Some of the cars tipped over.
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Human error has already been ruled out, Transport Minister Frederic Cuvillier told reporters Saturday, Praising the quick reflexes of the driver, who sent up the alert that halted all train traffic in the area.
President Francois Hollande said in an interview on Sunday that "we cannot rule out anything" while the investigation was ongoing. However, the French president said he believed an equipment failure was the most likely reason for the crash.
Attention is now focused on the switching system and a loose connecting bar.
The joint bar "broke away, it became detached and came out of its housing," Pierre Izard, general manager for infrastructure of France's state rail company, told AAP.
The faulty switch had been checked as recently as July 4. Railway officials immediately ordered checks of some 5000 similar joints on its network.
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Meanwhile, the search for survivors trapped in the crash wreckage continued through the night Friday and into Saturday.
While the death toll has not changed since shortly after the crash, rail officials said there's still a possibility that people could be underneath the overturned cars strewn across the rail tracks.
Passengers and officials in train stations across the country held a moment of silence at noon Saturday to commemorate the accident.