Barcelona attack witness: 'It reminded me of Bourke Street'

An Australian tourist has told of the horror that unfolded moments after a van ploughed into crowds in Barcelona, killing at least 12 people in a terrorist attack claimed by ISIS.

Susan McLean was about 100m from the scene as the van zigzagged down one of the city's busiest avenues, mowing down pedestrians and leaving bodies strewn across the ground.

"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," she told Nine Network 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.

"Then they just kept sort of - it was all in Spanish. It was very difficult to understand but they were sort of pushing us into shops."

Related: Twitter video shows van in Las Ramblas

Related: Crowds take cover in Barcelona shops

Two men have been arrested following the attack, which killed at least 12 people and injured over 80. 

It is currently the height of the tourist season in Barcelona, which is one of Europe's top travel destinations with at least 11 million visitors a year.