Mr Corcoran lives a five-minute drive from the tourist centre which was first hit by terrorists yesterday afternoon when at least one van was driven into the busy shopping area.
He has been working in Barcelona for the past four months as an English teacher.
He heard sirens as he walked home from work.
“I had about 20 missed calls from my mum and friends. When I was walking home the sirens were starting. In daily life you pass that way all the time, it’s where most of the shops are. It’s the main shopping place at the start of Las Ramblas.
“At the moment it is so full of tourists, kids, families, and people enjoying their lives. I just thought, ‘Oh my God how many people are there at the moment’.”
“It was shocking, just watching it. One of my friends further up from the area said everyone just started running.”
Corcoran added: “There were people with kids and people who would not have spoken the language, hearing the police shouting in Catalan or Spanish - that would have been very scary."
“You just feel helpless."
“When you wake up you don’t really want to go outside, but I’ll go out and go on with my normal routine otherwise you let the terrorists win."
“It is better to get on with your daily life, you could stay inside and be depressed, but then you're letting people who want to bring fear and terror win and that’s what they want to you do.”
Hours after the attack on Las Ramblas, five terrorists wearing suicide belts rammed civilians with a car in another Spanish seaside town before being shot dead by police in the second attack to hit the country.
Seven people including a police officer were injured during the incident in Cambrils, hours after a rampaging van driver left 13 people dead and over 100 wounded in Barcelona.
Bystanders ran for their lives as a gunfire broke out close to the coastal town's beachfront promenade early on Friday morning.
Residents of the popular tourist spot were ordered to take cover indoors as bullets tore through the air and footage later showed several lifeless bodies on the ground.
In the wake of the carnage several controlled blasts were carried out in the area, with police later saying the attackers had been wearing explosive belts.
Mossos, Catalonia's police force, said four of the attackers were shot dead at the scene and later confirmed a fifth had died of his injuries.
Of the six civilians caught up in the attack two were said to be in a serious condition.
Investigators said they are working on the theory that the attacks in Cambrils and Barcelona, as well as an explosion in the town of Alancar on Wednesday, are linked.