They did not stand a chance. As thousands of tourists enjoyed the late afternoon sun on a popular tree-lined avenue in Barcelona, a fanatic in a rented Fiat van came hurtling towards them.
Unsuspecting holidaymakers were sent flying into stalls selling souvenirs. Others were simply mown down as the terrorist zigzagged along the pedestrianised area of the tourist hotspot called Las Ramblas, the Daily Mail reported.
When he ended his murderous 500-yard rampage, dozens of bodies lay across the cobbled streets where thousands of families had been enjoying their holidays.
Some had been killed instantly. Shocked bystanders tried to tend to the catastrophic injuries suffered by dozens of others.
Amid the chaos, frantic mothers could be heard screaming the names of their missing children. At least one young girl is thought to have been killed.
Hundreds of tourists and locals fled in panic, seeking sanctuary inside shops, restaurants and churches amid fears that terrorists were still wreaking havoc.
Briton Susan Maclean, on holiday with her husband, described her 'unbridled fear' last night. "All of a sudden, there was this screaming and hordes of people, like a tidal wave of people, fear etched in their faces, running towards us, many of them yelling in Spanish," she told Channel 4 News.
"We had no idea what was going on. My first thought was this is a terrorist attack." The couple barricaded themselves inside a shop while they heard what sounded like gunshots outside.
Aamer Anwar, a criminal defence lawyer and Glasgow University rector, said he missed the attack by ten seconds.
"I was about to sit down and have something to eat... the place was jam-packed with tourists," he said. "Thousands and thousands of tourists. I walked on and about five, ten seconds later I heard a crashing noise, screams and it was almost like an avalanche - I just saw people running. I started running, people in front of me started to run, hundreds. People were screaming. People stated to panic.
"People were jumping into shops, pulling their children out of prams. There was no room [on Las Ramblas], it was swamped with families, children, and tourists. I saw a woman running. When we stopped she was screaming, because she could not see her children."
Ethan Spidey, 25, said there was a 'stampede' as tourists and locals sprinted away from the scene.
"I saw a young child knocked over and picked them up but everyone was just running," he said. "There was a stampede in the streets alongside Las Ramblas as everyone tried to run away. People were running into shops and taking refuge in cafes."
The carnage unfolded when the van mounted the paved middle section of Las Ramblas and gathered speed as the driver headed south towards the waterfront. Images of the aftermath showed several bodies lying on the street at the start of his rampage shortly after 5pm local time.
The fanatic, possibly travelling with an accomplice, continued to ram pedestrians before finally abandoning the white van on a street mural some 500 yards later.
He is thought to have fled through La Boqueria food market, which is popular with tourists and locals alike. Within minutes, armed police surrounded the area and carried out searches of every business as hundreds hid in shops, restaurants and churches.
Tom Gueller, who lives on a road adjoining the site of the attack, was forced to flee when the van began hitting pedestrians. "I heard screams and 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," he said.
Asked about the van, he added: "It wasn't slowing down at all. It was just going straight through the middle of the crowds in the middle of the Ramblas."
Steven Turner, who works in the area, told the BBC: "People in my office saw a van ramming into people on Las Ramblas. I saw about three or four people lying on the ground. About five minutes later I heard lots of screams from the crowd and then they dispersed."
Terrified witnesses told how they heard gunshots as armed police went shop-by-shop in search of their suspects.
British tourist Mel Higgins said: "I was barricaded inside a shop with my two daughters. We were walking down a parallel street when suddenly people started running towards us screaming 'Run!' and so I grabbed the two girls and ran inside an Orange phone shop.
"They locked the doors of the phone shop and we all waited there for around 20 minutes. We were just about to leave when everybody started running and screaming again. We went back inside and the staff shut down the shutters and told us to go upstairs."
Mrs Higgins was finally reunited with her husband some 25 minutes later.
Chris Pawley, 30 - who survived the Manchester Arena bomb - was yards from Las Ramblas when the carnage unfolded. He had been enjoying a trip to the Spanish city with his partner Corey Lorde.
He said: "We were caught up in the Arena attack - I can't believe it. There was police everywhere and ambulances, the shops started putting the shutters down."
A second van was later found in the town of Vic, 50 miles north of Barcelona. Police believe it was meant to be used as a getaway vehicle.