A man is on the run in Barcelona after what police say was a terror attack in the city centre.

A van ploughed into dozens of people in a square, according to police. The driver then jumped out and fled on foot, reports said.

Police told local news outlets that the two perpetrators may be holed up in a bar after having run from the attack.

The driver of the van is reported to have fled on foot and Spanish authorities have warned people to avoid the area. Eyewitnesses reported seeing people running away and screaming after the incident happened.

Police are looking for man who is 1.70 metres tall, wearing a white and blue striped shirt, El Pais reported.

Authorities described the incident on Twitter as a "massive crash". Emergency services said people should not go to the area around the city's Placa Catalunya, and requested the closure of nearby train and metro stations.

Aamer Anwar was walking down Las Ramblas at the time, which he said was "jam-packed" with tourists.

He told Sky News: "All of a sudden, I just sort of heard a crashing noise and the whole street just started to run, screaming. I saw a woman right next to me screaming for her kids.