A laptop caught fire and exploded on the MadridMetro injuring several passengers, it has been reported.
At least six people suffered minor injuries as smoke filled the carriage following the explosion – which police have confirmed was an accident.
The device also injured its owner, believed to be a woman who was carrying it in her bag, and led to passengers hitting the emergency brake.
The explosion, which took place near the Paco de Lucia at Principe de Vergara tube station, caused panic as commuters believed it was a terrorist attack, according to Spanish newspaper El Mundo.
Commuters had to get off the train and walk approximately 100m down the train tracks to safety.
Passenger Gonzalo Casatejada, 33, said people on the train were terrified.
"People started running, they said there was a backpack with smoke,” he told El Pais newspaper.
"We opened the door manually, we had been standing for several minutes, but people got scared and everybody started to run.
"We were afraid that it would be an attack."
Authorities were called to the scene and in a statement Spain’s national police confirmed the incident was an accident.
"Around ten police officers were deployed to the Príncipe de Vergara metro station after a portable computer caused a small explosion," the statement said.
"All those injured were attended to and everything points to an accidental cause to the incident.”
In 2004, Madrid was hit by a terrorist bomb attack on four trains that killed 192 people and injured around 2,000, the deadliest such attack in the country's history.
