Spain's second high-speed rail disaster this year, in which one train struck another from behind, killing 68 people, has raised fresh concerns about the safety of the country's rail network.

Search teams with sniffer dogs continued to look for victims on Thursday morning, a day after the collision in central Spain.

Cranes were in place to help shift the carriages as police and soldiers helped pick through the wreckage strewn down the gravel slope where at least three train carriages were tossed by the impact.