Pictures from the scene show armed police arrive in a cordoned-off area, while tourists and locals were evacuated from the busy Plaza de Catalunya.
Police officers and medics.
A person is seen being stretchered out of an evacuated shopping centre.
A police officer blocks the street to move people away from the area.
An armed officer arrives on the scene.
Armed police officers stand in a sealed-off area following the incident.
Abandoned balloons left by a street vendor in the Plaza de Catalunya.
Police officers move people back from the cordoned-off area.
Police officers assist an elderly woman as residents and tourists are evacuated.
All photos, unless otherwise stated: Pau Barrena and Josep Lago/AFP