Experts investigating the cause of a train crash in Spain that killed 40 people have found a broken joint on the rails.

The tail end of a train heading from Malaga to Madrid derailed at 7.45pm on Sunday, smashing into an oncoming train travelling from the capital to Huelva.

Investigators at the scene identified some wear on the joint between sections of the rail, known as a fishplate, which they said showed the fault had been there for some time, a source briefed on the investigations told Reuters.

They ‍found that the ‌faulty joint created a gap between the rail sections that widened as trains continued to travel along the track, which was renovated in May as part of a €700m (£608m) project.

Technicians believe the faulty joint is key to identifying the precise cause of the high-speed crash, the source added.

The first carriages of the train that derailed, operated by Spanish firm Iryo, drove over the gap in ‌the rails. But the eighth, ‍and last, carriage derailed, bringing with it the seventh and sixth carriages, the source said.

Credit: Civil Guard

Authorities are yet to establish an official cause of the crash, with Oscar Puente, the Spanish transport minister, calling the collision “truly strange”.

The Iryo train was less than four years old and passed an inspection on Jan 15.

Álvaro Fernández Heredia, the president of Renfe, the operator of the second train, ruled out the possibility of human error or excessive speed.

The speed limit on the track is 250km/h (149mph), while the trains were travelling at 210km/h and 205km/h when they collided.

In the months leading up to the crash, the company that manages Spain’s railway infrastructure warned of at least eight technical incidents on the high-speed line.

Most of the problems related to the signalling system, although there were also issues related to overhead power lines and other infrastructure.

The government was asked about the issues last summer and responded by saying it had addressed two “technical incidents affecting the signalling systems”.

Credit: Guardia Civil

In a statement, Iryo said it “deeply regretted what had happened” and that it had activated “all its emergency protocols”.

Authorities said there were 20 seconds between the Iryo train veering off the track and the subsequent collision, leaving the driver of the second train – who was killed in the crash – with almost no time to react before the impact.

Mr Heredia said the signalling and track-based safety mechanisms designed to detect an occupied track had no time to activate.

He also warned that determining the exact cause of the crash could take several days and that the circumstances were “rare and difficult to explain”.

The investigation is being led by the Commission for the Investigation of Railway Accidents, which operates within Spain’s transport ministry.

A separate judicial investigation has also been launched by a court in Montoro, Cordoba.

Juanma Moreno, Andalucia’s regional president, said: “It is likely [that more dead will be found] when you look at the mass of metal that is there. The firefighters have done a great job, but unfortunately, when they get the heavy machinery to lift the carriages, it is probable we will find more victims.

“Here at ground zero, when you look at this mass of twisted iron, you see the violence of the impact.”

Mr Moreno said that authorities were also searching the area nearby. “The impact was so incredibly violent that we have found bodies hundreds of meters away,” he added.

Video released by Spain’s Guardia Civil showed the sides of the worst-hit carriages shredded open, with train seats lying on the surrounding gravel.

One carriage lay on its side, bent around a large concrete pillar, with debris scattered around the area.

“There were moments when we had to remove the dead to get to the living,” Francisco Carmona, firefighter chief of Cordoba, told Onda Cero radio.

Javier Mesones, a 36 -year-old painter from Adamuz, said he heard about the crash on a WhatsApp group and set off with a friend to see if they could help.

The Guardia Civil did not let them access the crash zone in their car so the pair returned with a quad bike that became an unlikely rescue vehicle.

“There were people struggling to get clear of the wreckage and lying injured, so we pulled them onto the front rack of the quad and got them up the slope to safety – about 15 people,” Mr Mesones told The Telegraph.

“It was dark, sirens were blazing but what I saw was a catastrophe, a bloodbath. I’ve never seen anything like it in my life,” he added.

As well as the pain from wounds and injuries, passengers suffered from cold and shock on a night where the temperatures at the crash area dropped as low as 2C.

Agustín Pérez, another Adamuz resident, broke open a fence to allow vehicles access to a track that runs parallel to the railway to grant access to ambulances and rescue teams.

The 44-year-old owner of a wildlife tourism company said: “The thing that hit me hardest were the screams of pain from the carriages.”

Amid the chaos, Guardia Civil rescue workers found a six-year-old girl wandering alone with barely a few scratches on her head.

On Monday it emerged that the rest of the girl’s four family members who were travelling home to Punta Umbría in Huelva had died.

A sports centre in Adamuz was turned into a makeshift hospital, and the Spanish Red Cross established a help centre for emergency service workers and people seeking information.

“The scene was horrific. It was terrible,” Rafael Moreno, the mayor of Adamuz, told reporters. “People asking and begging for help. Those leaving the wreckage. Images that will always stay in my mind.”

Spanish King Felipe VI expressed his condolences, adding that the royal house was looking to visit Adamuz in the coming days.

“I understand the desperation of the families and the number of injured people who have suffered this accident, and we are all really worried,” he said.

On Monday, the Spanish flag was flown at half-mast in front of Madrid’s Parliament, while Pedro Sánchez, the country’s prime minister, visited the crash site.

Spain has spent decades investing in high-speed trains and currently has the largest rail network in Europe for trains over 155mph, with more than 1,900 miles of track, according to the European Union.

Sunday’s crash was the first with deaths on a high-speed train since Spain’s high-speed rail network opened its first line in 1992.