Chinese President Xi Jinping sent condolences to Greek President Katerina Sakellaropoulou on Wednesday over a deadly train collision in Greece.

In a message of condolence to Sakellaropoulou, Xi said that he was shocked to learn of the accident, which has caused major casualties.

On behalf of the Chinese government and people and in his own name, Xi expressed deep condolences for those killed in the accident and sincere sympathies to the bereaved families.

He wished the injured a quick recovery.

Greek officials on Wednesday said a train carrying hundreds of people collided at high speed with an oncoming freight train in a fiery wreck in northern Greece, killing at least 36 people and injuring dozens.

Multiple cars derailed and at least three burst into flames after the collision near the town of Tempe on Tuesday just before midnight. Rescue crews illuminated the scene with floodlights before dawn on Wednesday as they searched through the twisted, smoking wreckage for survivors.

Survivors said several passengers were thrown through the windows of the train cars due to the impact. They said others fought to free themselves after the passenger train buckled, slamming into a field next to the tracks near a gorge about 380 kilometers north of Athens where major highway and rail tunnels are located.

"There were many big pieces of steel," said Vassilis Polyzos, a local resident who was one of the first people on the scene. "The trains were completely destroyed, both passenger and freight trains."

Dazed and disoriented people were escaping out of the train's rear cars as he arrived, he said.

"People, naturally, were scared — very scared," he said. "They were looking around, searching; they didn't know where they were."

Costas Agorastos, the governor of Thessaly, told Greece's Skai television that the two trains crashed head on at high speed.

Rescuers wearing headlamps worked in thick smoke, pulling pieces of mangled metal from the cars to search for trapped people. Others scoured the field with flashlights and checked underneath the wreckage. Several of the dead are believed to have been found in the restaurant area near the front of the passenger train.

Sakellaropoulou said on Wednesday she was cutting short a visit to Moldova to return to Greece following the collision. She announced her decision at a news conference in Moldova.

The cause of the collision was not immediately clear. The station master in the nearby city of Larissa has been arrested and another two people have been detained for questioning.

Agencies contributed to this story.