Serious flaws in a signalling system caused a fatal crash on China's high-speed rail network, officials say.
Thirty-nine people died last Saturday when a train ran into the back of another which had stalled on a viaduct near Wenzhou after lightning cut its power supply.
The system "failed to turn the green light into red", said An Lusheng, head of the Shanghai Railway Bureau.
Chinese Premier Wen Jiabao, who has been visiting the crash site, vowed to "severely punish" those responsible, the BBC reports.
Six carriages derailed and four fell between 20 to 30 metres from the viaduct after the crash, which injured nearly 200 people.
The accident came just four years after China's first high-speed trains began operating.
Rail experts had warned against the rush to build the world's longest and fastest high-speed rail network in record time amid safety concerns.
There are allegations that corners were cut during construction because of corruption, raising questions about infrastructure throughout the country.