Catalan police said a police operation against a possible "terrorist attack" was ongoing in the town of Cambrils, south of Barcelona.

It was not clear how the operation was linked to the van attack in Barcelona on Thursday that has left so far 13 people dead.

READ: Van ploughs through crowd in Barcelona, killing at least 13

Catalan emergency services said on Twitter that people in Cambrils, which is on the coast, should "stay home, stay safe."