Most of the injuries were slight but five people were hospitalized following the accident shortly after midnight Thursday at the Puerta del Sol station, the city's emergency rescue service said.
A train which had just taken on passengers and was preparing to leave was struck from behind by an empty train whose driver had failed to see a red light.
The empty train was moving at less than 20 kph (13 mph) because of a mechanical problem, but still triggered panic in the train it hit. Passengers screamed and tried to claw doors open, newspapers reported.
"It was a tremendous bump. It pushed an entire car into the tunnel," Miguel Jimenez, driver of the train that was hit, told El Pais.
Putin's official spokesman Dmitry Peskov commented on remarks in the US media about failures in launching nuclear-capable missiles in Russia
More than 5.8 million people voted for Nicholas Maduro at the presidential election in Venezuela. This is more than a quarter of registered voters. Why did those people vote for the man, who, as Western media write, took Venezuela to the brink of collapse?
It has long been understood that the West has been trying to subject Russian borders to total control. We have not seen such activity even during the Cold War