Barcelona terror: Aussie witnesses describe 'absolute carnage' with 'bodies everywhere' after van attack

Australian witnesses have described the horrific moment a van ploughed into dozens of tourists on Barcelona's most famous street.

Young Perth traveller Jesse Montile and his girlfriend had just got off the plane and were looking for an Airbnb when a white hire van ploughed into pedestrians, killing 13 and leaving dozens more injured.

“I saw police running down roads and streets and alleyways with guns including on motorbikes and big vans while wearing bullet proof vests,” Mr Montile told 7 News Online.

“I got pulled into shops and had to hide in a down stairs bunker type thing.”

Cyber security expert Susan McLean was just 100 metres away when the horror unfolded.

"All of a sudden, scores of people ran towards us -- hysterical, children hysterical. They first of all said someone had been shot," Ms McLean told 7 News.

"It calmed down for a moment then all of a sudden a second wave of people came down the street. Our hotel was one street away so we got ourselves out," she told Sky.

"We could see the police, we could see all the cars stopped.

Barcelona's most famous street was packed with tourists when a van drove into the crowds on a sunny Thursday afternoon, leaving scenes of carnage and panic.

"There were bodies everywhere on the ground with people crowding round them. People were crying," witness Xavi Perez added.

The region's interior minister gave a grim toll from what police said was a terror attack: 13 dead and more than 100 injured.

Among the foreigners caught up on Las Ramblas was Aamar Anwar, a renowned Scottish human rights lawyer in Barcelona for a conference, and he had been walking down the boulevard when the terror unfolded.

"All of a sudden I heard a crashing noise and the whole street just started to run screaming," he told Sky News, describing a scene of thousands of people struck by chaos and panic.

"I saw a woman next to me screaming for her kids.

"Literally within 30 seconds, police vans, ambulances, police officers with guns were piling out, and we were sectioned off and then being pushed rapidly back," he said.

Another witness said he saw a man fleeing.

"I saw a man run down the Ramblas, with police chasing him and he appeared to drop a black metal object. It looked like a pistol," said the witness who only gave his first name, Sergio.

Another man at the scene told Spanish television channel TVE that he saw the suspect.

"It was a person in their 20s, he was very young, brown hair, a slim face. I saw him when the van stopped. We were very close to everything."

As people ran for their lives they were replaced by armed police officers who sealed off the scene.

"Van upon van of police officers" then arrived, Anwar said. "They have quite clearly unfortunately had to plan for something like this."