WATCH: Scenes of horror after van smashes into crowd in Barcelona

Horrific video footage has emerged of the immediate aftermath of a suspected terror attack on Thursday in Barcelona, Spain, which left at least 13 people dead and 80 injured.

The video shows bloodied and battered victims lying in the street in the popular tourist area of Las Ramblas shortly after a rented van ploughed into the crowd on Thursday afternoon. 

Aamar Anwar, a renowned Scottish human rights lawyer, was 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.

Catalonia's regional head told Reuters that Spanish police had arrested two people.

Spain's royal family condemned the assault in unusually strong terms, vowing that their country would not be "terrorised" by extremists.

British Prime Minister Theresa May as well as US President Donald Trump have condemned the attack.

May, the Guardian reported, said the UK “stands with Spain against terror”.

Spanish police meanwhile released an image of a suspect they said had rented the van used in the attack.

Facebook activated its "safety check" feature to allow friends and families to check on their loved ones in Barcelona.

- Additional reporting by AFP