Deliberate car ramming by man in a town east of Paris killed one adolescent girl and injured at least 13 other people.
At least 13 people have been killed, and scores were injured after a white van ploughed into a crowd in Barcelona’s busy tourist area, officials said.
Joaquim Forn, Catalonia’s interior minister, confirmed the death toll on Twitter.
At least 80 people have been hospitalised, Catalonia’s regional head Carles Puigdemont told a news conference.
Police said at least 10 of the injured sustained serious wounds, describing Thursday’s incident as a “terrorist attack”.
Puigdemont said that Spanish police had arrested two people as they dismissed earlier reports of suspects holed up in a nearby bar.
The suspected driver of the van mounted a pavement at around 5pm local time (15:00 GMT) in the city’s iconic Las Ramblas area, which is full of shops and restaurants.
El Pais newspaper said the driver of the vehicle had fled on foot after the attack.
It was still not clear how many attackers had been involved in the incident.
After the attack, people were warned against travelling to Placa Catalunya as Facebook activated its “Safety Check” tool.
Nafees Hamid, a witness, told Al Jazeera: “There are helicopters everywhere above, and armed police are rushing into the area. Police have cordoned off Las Ramblas.”
He explained by phone that most people heeded a police warning to go inside while the situation was active.
Other witnesses spoke of a scene of carnage, with bodies strewn along the boulevard as others fleeing for their lives.
“When it happened I ran out and saw the damage,” local shop worker Xavi Perez told AFP news agency. “There were bodies on the floor with people crowding round them. People were crying. There were lots of foreigners.”
Witness Aamer Anwar told Britain’s Sky News television that he was walking down Las Ramblas, which he described as “jam-packed” with tourists.
“All of a sudden, I just sort of heard a crashing noise and the whole street just started to run, screaming. I saw a woman right next to me screaming for her kids.”
Video posted to social media showed emergency services at the scene.
Spanish Prime Minister Mariano Rajoy said he was in contact with authorities and was on his way to the city.
Emergency services asked Metro and train stations to close, according to reports.
The alleged attack took place at the height of the tourist season in Barcelona, which is one of Europe’s top travel destinations with at least 11 million visitors a year.
Meanwhile, a second van linked to the attack was found in the small town of Vic in Catalonia, local authorities there said on Twitter.
Catalan police said a driver earlier hit two officers in Barcelona, but it was unclear whether this incident was related to the early evening attack in Las Ramblas.
Secretary of State Rex Tillerson sent condolences and offered US assistance to Spanish authorities.
Speaking to reporters, Tillerson said the incident “has the hallmarks of what appears to be yet another terrorist attack”.
French President Macron expressed France’s solidarity after what he termed a “tragic attack”.
German Chancellor Angela Merkel described the incident as “a revolting attack”.
British Prime Minister Theresa May condemned the “terrible” attack and said the UK “stands with Spain against terror”.
European Commission President Jean-Claude Juncker expressed his “profound sorrow and anguish” at the attack.
“This cowardly attack has deliberately targeted those enjoying life and sharing time with family and friends,” Juncker said. “We will never be cowed by such barbarism.”
Pope Francis said he was praying for the victims.
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 attacks across Europe, killing more than 100 people in Nice, Berlin, London and Stockholm.