Witnesses to the terror attack in Barcelona described how a white van hurtled through crowds without slowing down.
Scores were sent scattering in panic as carnage unfolded on Las Ramblas, a bustling high street often thronged with tourists.
Many were forced to take shelter in nearby shops, while others reported hearing gunshots.
Tom Gueller, who lives on a road adjoining the site of the attack, was forced to flee when the vehicle began hitting pedestrians.
He told BBC's PM: "I heard screams and a bit of a crash and then I just saw the crowd parting and this van going full pelt down the middle of the Ramblas, and I immediately knew that it was a terrorist attack or something like that.
"I ran away, I mean I live near, I had to run back about 50 metres or so and go up to my flat and obviously see what's happening on the road from my balcony."
Asked about the van, he said: "It wasn't slowing down at all. It was just going straight through the middle of the crowds in the middle of the Ramblas."
Video captured by eyewitnesses and circulating on social media showed the bloody aftermath of the incident.
At least 19 victims, some bleeding heavily, were visible in one clip - lying amid piles of souvenirs apparently sent flying in the chaos.
Havoc descended on the Catalan city at the height of tourist season.
Will Ako, 26, from London, was eating in a restaurant called Taller De Tapas with his family when they heard a disturbance.
He told the Press Association: "We had just finished eating and were about to leave when we heard a commotion and the patrons in the restaurant rushing from their seats.
"I then saw people running to the east of the restaurant and I saw a couple of people, about 30 yards down the road, crouching around what looked like someone on the ground and they were calling for assistance.
"Within a couple of minutes, police started to arrive and they were running west of the restaurant and some were telling us to stay inside.
"Soon after, loads of cars, bikes and ambulances arrived and then the armed police."
He said he was in the restaurant with around 40 people, adding: "We're not sure what's happening."
Tourist Mel Higgins told Sky News she was barricaded into a shop with her daughters at the time of the incident.
She said: "I was with my two daughters and we were walking down the Passeig de Gracia, which is sort of parallel and one up from Las Ramblas, when suddenly people just started running towards us, screaming and shouting: 'Run! Run! Run!'.
"So I grabbed the two girls and there was an Orange phone shop was open and we ran inside and they locked the doors of the phone shop, and we just all waited there for I suppose about 20 minutes.
"And then it seemed very calm out on the street. And obviously the people working in Orange were in touch with the police and the police said just stay there for now.
"Then about 20 minutes later, they said we could leave and we were just about to leave when people started running again, and screaming, and they said: 'Everyone back in!'."