The regional government said around 30 people have been killed. CNN reported at least 34 were dead.

More than 20 people are believed to have been seriously injured. Unconfirmed reports said a number of people were still trapped in the metro train which derailed between two stations.

Two carriages have overturned, reports said. The accident happened at 1 p.m. local time on Monday and the cause is still unclear. But officials ruled out a terror attack. The derailment triggered memories of the train bombings by Islamist militants that killed 191 people in Madrid in 2004.

"It seems this unfortunate accident was caused by excess speed and a wheel breaking just before it entered the station," government official Luis Felipe Martinez told Spanish radio, adding that the number of dead was still not confirmed, Reuters reported.