"Police officers who got there just started screaming at people to move back, move back".
Police have confirmed that the "massive crash" involved a white van mounting the pavement.
Las Ramblas, a street of stalls and shops that cuts through the center of Barcelona, is one of the city's top tourist destinations.
'The central intelligence agency moved its notice to the Catalan autonomous police two months ago.
Today's attack also comes just days after a white supremacist drove his auto into a crowd of counterprotesters during the "Unite the Right" rally in Charlottesville, VA. Authorities have called the incident a "terrorist attack".
Update: Sky updates to say that El Pais is now also confirming 13 dead - at least. And a reported shootout is taking place in a Barcelona market.
There's video circulating of victims in the aftermath but it's graphic.
Below is the van that was used in the attack. An eyewitness told a Spanish TV station that the suspect was running people over in a van for almost 1,000 feet before fleeing into a nearby Turkish restaurant. Although reports and facts are still being pieced together, an apparent van-based terror attack in Barcelona, Spain has resulted in a dozen fatalities and approximately 80 injuries, according to media reports and government accounts.
The reported death toll has now climbed to 13 people, and now there is a second scene that may be related to the vehicle attack.
UPDATE (12:54PM): First Lady Melania Trump reacted to the terrorist attack in Barcelona. A second van linked to the attack - assumed to have been used as getaway auto - has been found in the small town of Vic in Catalonia.
Barcelona's Tv3: also reported the Spanish passport of a person of Moroccan origin was found at the scene of the attack. In a photograph on public broadcaster RTVE, three people were lying on the ground in the street of the northern Spanish city Thursday afternoon, apparently being helped by police.
The president of Spain's Catalonia region says police have arrested two people. He vowed the United States would never relent in tracking down terror suspects and holding them to account.
Spain's royal palace has condemned the deadly van attack in Barcelona, calling the perpetrators "assassins, simply criminals who will not terrorise us".
"We extend our deepest condolences and wish fortitude to the families of those who lost their lives, and speedy recovery to those wounded in these heinous attacks which display once again the brutal face of terrorism, and target all humanity". It is unknown if this attack involves more than two individuals. The ISIL terror group claimed responsibility for both.
The terror suspect is a Moroccan citizen and a legal resident in Spain.