Four Australians have been confirmed injured after a van ploughed into crowds of pedestrians in a busy tourist district in the heart of Barcelona, with one woman hospitalised in a “serious” condition.

Australian tourist Susan McLean, who was separated from her husband in the panic, was about 100 metres from the scene and spoke of the horror that unfolded moments after the attack.

“All of a sudden there was this tidal wave of people running from both Placa de Catalunya and Las Ramblas towards us screaming, crying and with absolute terror etched on their faces,” Ms McLean told Channel Nine on Friday.

“Initially we couldn’t hear anything other than all these people running towards us. Several of them were calling ‘gun, gun’, so first of all we thought someone had been shot.

“It was all in Spanish. It was very difficult to understand but they were sort of pushing us into shops.”

• BARCELONA TERROR: WHAT WE KNOW SO FAR

Ms McLean said the scene reminded her of Melbourne’s January 20 Bourke Street Mall attack.

Melbourne Fire Brigade Commander Graeme O’Sullivan — who was a first responder to the Bourke Street massacre — was with his wife at a Barcelona restaurant bar at 5pm when they heard the “horrific screams” of people trying to escape the attack.

“Then, we heard a number of loud thuds and screaming which turned out to be the sound of people getting hit,” he told the Herald Sun.

Melbourne woman Alana Reader, 26, was in one of the stores overlooking the area where the van entered.

“All of a sudden hundreds of people turned around and were screaming and running in all kinds of directions,” Ms Reader told Rafael Epstein on ABC Radio Melbourne.

“Other people were banging on the door to try and get into the store.

“I’ve never been that terrified in my life, I just ran.”

A woman cries after a van ploughed into pedestrians, killing at least 16 people. Photo: Getty

Australian Gil Van Der Venne told 3AW he saw the attack unfold from his hotel balcony.

“We’re looking over the balcony … and there it is all happening in front of you,” he said.

“There were at least five bodies that I saw, at least three of them are still there now with body bags, so you’d imagine they’ve passed.

“The van, I believe, had probably travelled about three-quarters down Las Ramblas.”

Foreign Affairs Minister Julie Bishop condemned the attack and confirmed one Australian woman was injured, while two men were “directly affected”.

She said the woman, believed to be from New South Wales, was in a “serious but stable” condition. The men are believed to be from Victoria.

“They’re in direct contact with consular staff. They have advised they were directly affected. I’m not sure if they have been injured or if they just need to see a medical professional,” Ms Bishop said.

She confirmed at 2.30pm that a second woman, believed to be from NSW, was in a “serious condition” in hospital. She had been travelling with a British passport.

“Two (others) were the young men from Victoria, who, I understand, were actually hit by the car in one instance,” Ms Bishop told reporters on Friday.

“They have received treatment at hospital, but both have been discharged.”

It’s understood the van grazed the men rather than hitting them square on.

Prime Minister Malcolm Turnbull said Australian consular officials were on their way to Barcelona from Madrid.

“Our love, our prayers, are with the victims and their families,” Mr Turnbull said.

“We stand in absolute resolute solidarity with the people of Spain in the fight against Islamist terrorism. This is a global battle against terrorism.”

At least 16 people have been killed and 100 injured in Barcelona. Local police said they were treating the incident as a terror attack.