The late afternoon attack in the city's Las Ramblas district left victims sprawled in the historic street, spattered with blood or writhing in pain from broken limbs.
"I saw a lot of ambulances, I saw a lot of emergency vehicles nearly immediately", he said. In Spain, there hasn't been a major terrorist attack since the 2004 Madrid train bombings by Al Qaeda inspired terrorists, according to El Pais.
The driver of the van fled the scene on foot.
Police are attributing the incident to terrorism.
Police said they arrested two men, a Moroccan and a man from Spain's north African enclave of Melilla, though neither was the driver.
It was another provocative tweet from an increasingly isolated leader who uses Twitter to take shots at perceived opponents - and even announce big policy changes.
"We confirm the terrorist attack", Catalan police said.
"Whoever is responsible should know the United States of America, along with our allies, will find and punish those responsible and drive the evil of radical Islamic terror from the face of the Earth", Pence said. The terror group has not mentioned any names nor did it post any photos or additional details about the perpetrators.
In a joint press conference with Panamanian president Juan Carlos Varela, Vice President Pence offered his condolences to Spain after a deadly terrorist attack in Barcelona on Thursday.
Mr Willis said the attack had taken an obvious toll on the community with everyone on knife-edge and children crying in fear.
"There are a lot of police officers".
It was still not clear how many attackers had been involved.
One person was killed in an explosion in a house in Catalonia, according to Spanish police.
The scene after a van plowed into a crowd, injuring several people in Barcelona. Earlier, Spanish police described the carnage as "massive". The Catalan Interior Ministry said late Thursday that a vehicle broke through a police checkpoint outside Barcelona and injured two police officers.
That's when it crossed her mind that if, say, a bomb were to go off, there "would be so many people hit, it's such a popular spot".
Authorities said the dead included a Belgian and a Greek woman was among the injured.
ISIS often claims responsibility for such attacks, even when they turn out to be carried out by individuals with no connection to the extremist group.