A group of children were being held hostage at a school near Barcelona this afternoon, the government said.
The Interior Ministry said details were unclear but the motive appears to be money.
A spokesman declined to confirm reports that there were three assailants with knives holding 25 children aged 12.
He said there was at least one assailant but the number and age of the children was not immediately known.
Three ambulances raced to the Casal de l’Angel school in Hospitalet de Llobregat, an industrial town just south of Barcelona.