The only thing Alana Reader could do was hide. She dived behind a clothing rack, lay flat on the floor, and feared for her life.

"I was thinking 'this guy could drive through the front windows and where would we run to if they jumped out with knives or guns?'

"All I wanted to do was crawl home and call my parents and my family."

Mr Reader is holidaying in Barcelona with her two friends Julia Monaco and Julia Rocca. A fourth friend, Steph Lamb, had been in Italy with them but did not join them in Spain.

The three Melbourne friends - all aged 26 - were minutes from leaving the retail store Urban Outfitters on Placa de Catalunya when they saw people "running and screaming with genuine fear".

"We were about to leave the store and they locked the doors," Ms Reader told ABC Radio.

Unbeknown to them at the time, a white van had careened through the popular Las Ramblas tourist boulevard, killing at least 16 people and injuring more than 100 others.

Ms Monaco told radio station 3AW initial confusion inside the store gave way to panic.

"All of a sudden we were locked in the shop and confusion started ... nobody was really sure what was happening," Ms Monaco said.

"The music was still playing in the shop ... suddenly we could see that the police presence was rapidly increasing. Then we started seeing people looking incredibly distressed.

"The next second we knew, we were literally running for our lives to the very back of the store where we were told to get on the ground, away from the windows and just lay as flat as possible.

"We hid behind a clothing display that was about knee-high. There was considerable panic. There were two children who were screaming."

The friends spent about 20 minutes lying on the floor with an Israeli family, a British family and a German girl.

"I've never been so terrified, it's a feeling I'll never be able to describe and hope I never experience again but so grateful I'm alive," Ms Reader wrote on Facebook.

She later told the ABC: "We haven't come to terms with it. It's surreal. The sheer fear is quite incredible."

Despite their ordeal, the trio plans to continue their trip.

Ms Monaco insisted she wouldn't take her parents' advice and cut her four-month European adventure short.

"I feel a bit rattled ... but I don't feel like I want to go home ... I don't want to let 'them' win. I'll finish what I started," she told 3AW.

"[I] still want to travel the world, maybe there's something wrong with me but I'll keep going."

Three Australians were injured in the attack: a NSW woman and two young men from Melbourne's western suburbs.

The woman is in a serious but stable condition in hospital. The Melbourne men have told Australian consular staff they were injured, but returned to their hotel with plans to get medical treatment on Friday morning, local time.

It is believed they were hit by the speeding van.

"I understand [they] were actually hit by the car in one instance. But have received treatment and been discharged [from hospital]," Foreign Minister Julie Bishop told reporters.

Melbourne man Michael Christou was about 300 metres from the initial scene of the Las Ramblas carnage and was also nearby when eight people, including two Australians, were killed in the London Bridge van attack in June.

"I think it's following me but you kind of come over here [to Europe] and you expect it to happen but you don't let it stop you from doing what you want to do."

A Geelong man has told 3AW of his "sliding doors" moment. The man, "Barry" told the station that he had left the smaller exit of the raiway station close to La Ramblas.

"Suddenly just waves of people starting running to us, screaming, and just terrified," he said.

"Police were taking control and virtually herding them across the street.

"I can't tell you the sense of mayhem that pervaded."

Barry said he hid in a hotel for about five hours, and was planning to return to Australia "as soon as possible".

- with AAP