At least 68 people were killed on Wednesday morning in a high-speed train collision along the railway linking Madrid and Andalusia, Spanish media reported.

Spanish Transport Minister Oscar Puente confirmed that a computer safety system breakdown halted all trains along a 63-kilometer section at around 8:30 a.m. Minutes later, railway control center staff mistakenly authorized a high-speed train to override a red signal. The train traveled nearly 25 kilometers before slamming into the rear of a stopped train ahead, sending two carriages plunging down an embankment.

The national infrastructure agency has suspended all rail services on the line, while Spanish Prime Minister Pedro Sanchez announced three days of national mourning and pledged a thorough investigation into the tragedy.