A van crashed into dozens of people in the centre of Barcelona this afternoon and according to initial reports, two people were killed and several were injured.
Police described the incident on Twitter as a "massive crash" and later spoke of 'terrorism'.
Emergency services said people should not go to the area around the city's Placa Catalunya, and requested the closure of nearby train and metro stations.
El Pais newspaper said the driver of the vehicle had fled on foot after mowing down dozens of people.
Local media said two armed men had also entered a restaurant in Barcelona. El Periodico reported gunfire in the area of La Boqueria Market, although it did not cite the source of the information.
It was not immediately clear that the men were the drivers of the van.
While full details of the incident were not immediately clear, since July 2016 vehicles have been used to ram into crowds in a series of militant attacks across Europe, killing well over 100 people in Nice, Berlin, London and Stockholm.
In recent weeks, threatening graffiti against tourists has appeared in Barcelona, which draws at least 11 million visitors a year.
In one video released under the slogan "tourism kills neighbourhoods", several hooded individuals stopped a tourist bus in Barcelona, slashed the tyres and spray-painted the windscreen.