(Edited by: Wesley Rahn)

Spain began three days of national mourning on Thursday in remembrance of the 68 people killed in one of Europe's deadliest train disasters in recent memory.

On Wednesday morning, a high-speed train run by state operator RENFE slammed into the back of a stationary train operated by private Spanish company Iryo in the central region of Castilla-La Mancha, south of Madrid.

A British tourist who was rescued from the RENFE train told the Associated Press that "suddenly, everything started falling apart."

"We realized carriage two, carriage one, all gone, all smashed. There was blood all over," the man said.

Emergency crews work through the night

Emergency crews continued searching through the wreckage overnight for survivors and bodies, using cranes to move mangled metal.

Relatives of passengers gathered at nearby facilities seeking information about missing loved ones.

Residents of the nearby town of Urda joined emergency workers in helping survivors, providing first aid supplies, water and blankets.

Teams of Red Cross workers offered support.

Red Cross psychologist Carmen Garcia told AFP news agency that many people are in shock and "haven't taken on board what has happened."

"The grieving will be complicated," Garcia said.

Authorities are collecting DNA samples from relatives in Madrid, Toledo, Cordoba and Seville to help identify the missing.

Spain's rail network safety in question

Wednesday's crash was Spain's second high-speed rail disaster this year and has raised fresh questions about rail safety.

Transport Minister Oscar Puente blamed the crash on an "inexplicable" decision to allow one train to continue after an automatic control system failed along a stretch of track.

He said the RENFE high-speed train had travelled about 25 kilometers before hitting the stationary Iryo train.

Prime Minister Pedro Sanchez, who visited the crash site, pledged a full investigation and measures to strengthen rail safety.

"It is clear that we need to reinforce the safety of our train service to rebuild the trust in our high-speed rail," Sanchez said. "It is not acceptable for a country like Spain to endure two high-speed train accidents in the same year."

In January, 46 people died when a high-speed train derailed and collided with another in the southern Andalusia region.

The latest disaster comes just weeks before Spain's November 29 general election.