A high-speed passenger train derailed and crashed into another train in southern Spain on Tuesday evening, killing at least 21 people and injuring dozens more. It was one of the deadliest rail accidents the country has seen in recent years.

The back section of a train traveling from Malaga to Madrid, carrying about 300 passengers, left the tracks near the city of Córdoba at around 7:45 p.m., according to rail operator Adif.

 It then struck an oncoming train heading from Madrid to Huelva with roughly 200 passengers. Several carriages were thrown off the tracks and slid down a four-metre embankment, Bloomberg reported.

Spain’s transport minister, Óscar Puente, said the cause of the crash was still unknown and called the incident “very unusual.” The accident happened on a straight, flat section of track that had been renovated just a few months ago. Officials warned that the number of dead could still increase.

 Reports show that some used emergency hammers to break windows and climb out of damaged carriages. Videos from the scene showed people crawling through windows as train cars leaned at sharp angles. Many survivors escaped in the dark, some without serious injuries.

The crash happened near the village of Adamuz, an area that is difficult to reach. Rescue workers spent hours helping hundreds of passengers get to safety. Local residents brought blankets and water to help those affected. Andalusia’s regional president, Juanma Moreno, said 75 people were taken to hospital, including 15 who were seriously injured, most of them in Córdoba.

Fire officials said one of the trains was badly damaged, with at least four carriages completely off the rails. Emergency teams from the military, civil protection services, the Civil Guard and the Red Cross were sent to the scene. The Red Cross also set up a help centre in Adamuz for families and survivors.

Prime Minister Pedro Sánchez expressed his condolences, calling it “a night of deep sadness for our country.”

An official investigation has begun, but the transport minister said it could take up to a month to find out exactly what caused the crash, a troubling situation for a country known for its modern and reliable high-speed rail system.