It is not known whether its connected to the attack in Barcelona, in which 13 people died and dozens more were injured when a van drove at crowds in the bustling La Ramblas area of the city on Thursday afternoon.
Police are still looking for the driver of the van, while two arrests have been made.
The vehicle drove at speed through the boulevard mowing down pedestrians in what Spain's prime minister has described as "jihadi terrorism".
Police confirmed in a press conference on Thursday evening that more than 100 people were injured following the incident. At least 15 of those injured are thought to be in a critical condition and the death toll is expected to rise.
ISIL have claimed responsiblity for the attack, which targeted a boulevard popular with tourists in the height of the summer.
Belgium's deputy Prime Minister confirmed on Twitter that a Belgian national was one of the victims killed in the attack.
Nous devons malheureusement déplorer une victime belge à #Barcelone J'adresse mes condoléances à sa famille et à ses proches.
The driver of the vehicle fled the scene on foot, and police have instituted a manhunt for him, calling the attack a terrorist incident.
Police have released an image of a man alleged to have rented the van. He has been named as Driss Oubakir, reported to have been born in Morocco by local media.
Catalan police have also said that hours after the attack a driver struck two officers at a checkpoint. Although it is not known whether it is related to the van attack.
Local media are reporting that a suspect was killed during a shoot-out with police.
Police said that an explosion at a house outside Barcelona on Wednesday in which one person died was connected with the attack.
Gunfire was heard in the area round La Boqueria market as of 4.50pm local time, according to media.
It was suggested earlier on on Thursday that two men had entered a restaurant in the city and were appeared to be set upon remaining in a siege situation - police later denied these reports.
Witnesses speaking about the first incident described the chaos that ensued after the event.
Videos have circulated on social media showing many of the injured lying across the street as passersby rush to their aid. Police have urged social media users not to share graphic images from the scene.
Lindsay Davidson told Sky News: “We were in a changing room in a shop and saw loads of people running out the door, and we waited a few minutes to see what it was, then we came out the door and there were police everywhere. We didn’t see any victims, everyone was just running to escape the scene.
“All the shops are now shut, and all the cafes are closed tonight”.
If you are in the area of Plaça Catalunya in #Barcelona please stay put until the police say it's safe to move #Rambles
Eyewitness Susan McLean told the channel that it was “quite terrifying, all of sudden people ran screaming towards us, everyone hysterical. It calmed down for a moment than a second wave of people came down the street and we just ran. The police were doing their job but we had no idea what was going on.”
A photograph shown by public broadcaster RTVE, showed three people lying on the ground in the street apparently being helped by police and others.
Police cordoned off the broad, popular street, ordering stores and nearby Metro and train stations to close. They asked people to stay away from the area so as not to get in the way of emergency services. A helicopter hovered over the scene.
Las Ramblas, a street of stalls and shops that cuts through the center of Barcelona, is one of the city's top tourist destinations. People walk down a wide, pedestrianized path in the center of the street, but cars can travel on either side.
#Barcelona#Rambles If you are ok, please Inform your family using social networks to avoid the collapse of phone lines