At least six people are reported to be injured after a mobile device exploded in the subway of the Spanish capital here Monday morning, according to local media reports.

According to 20 Minutes, a Spanish newspaper, the National Police said the device was a portable computer while the Madrid Municipal Police said it was a mobile phone, which exploded at around 9:15 am local time (0715 GMT) on a train at the Principe de Vergara station on Line 9 of the city's metro system.

"A passenger's mobile phone exploded and burned the bag in which she was carrying it," said the Municipal Police, adding that "between five and six people needed emergency services for smoke inhalation."

Posts by witnesses said on Twitter that the explosion caused panic and a stampede among passengers.

Emergency services, including the fire brigade, ambulances and policemen rushed to the scene.

The metro service was halted for 15 minutes as a result of the incident, but has returned to normal at press time.