A violent jolt, followed by screams, flying objects, blood and then darkness is how survivors of the train crash in southern Spain on Sunday night described the moment of impact in the high-speed collision that killed at least 39 people.

The trains were carrying about 400 people when the accident happened near Adamuz in the province of Cordoba, about 360 km (223 miles) south of the capital Madrid. It left 122 people injured, with 48 still in hospital and 12 in intensive care, according to emergency services.

Most survivors said on Monday they were unaware of the scale of the disaster until they made it outside and witnessed injured or dead passengers, and rescuers working under floodlights beside the tracks.

"I started to get up and thought, this isn't normal. Then I looked for my sister. That's the last thing I remember before everything went dark," said Ana Garcia Aranda, 26, who was travelling to Madrid from Malaga with her sister and their dog after visiting family.

Other passengers had broken windows and pulled her from the wrecked carriage.

"There were people who were fine and others who were very, very badly injured. You had them right in front of you and you knew they were going to die, and you couldn't do anything," she said, wearing sticking plasters on her face.

Firefighters later rescued her sister from the train and took her to hospital, where she is in intensive care.

Outside the crash site, sirens echoed through the night as emergency vehicles flooded the narrow roads. Residents of Adamuz said the whole town mobilised, bringing water, blankets and food to help the stranded passengers.

"That won't be forgotten," Salvador Jimenez, a journalist with Spanish public broadcaster RTVE, who was pulled from one of the trains, said. "In the end, it's a lottery. Many of us were lucky."

Paqui, who owns a farm in the area and rushed to the site with her husband, recalls horrific scenes in and around the trains.

"Pieces of people, it wasn’t people anymore, you found arms. My husband saw a child who died inside... another child calling for his mother, looking for his mother," she said. "I can’t sleep, those are images that stay with you."

Another passenger, Raquel, told radio station Cadena Ser: "I was thrown from the back cabin and opened the door with my head," she said, adding that she briefly lost consciousness before managing to walk towards where firefighters were working.

Reporting by Nina Lopez, Michael Gore, Leonardo Benassatto, Susana Vera, writing by Jesus Calero, editing by Andrei Khalip and Sharon Singleton