The attack happened shortly after 5pm local time on Thursday when a white Fiat van tore through Las Ramblas, a major tourist attraction.
It was packed with families and holidaymakers, in a horror described as “jihad terrorism” by the country’s prime minister Mariano Rajoy.
Many killed and injured were browsing stalls selling tourist souvenirs along an avenue that stretches more than a kilometre towards the sea.
A major manhunt for the suspected driver was continuing on Friday.
Hours after the Barcelona rampage, a second terror attack happened around 60 miles away in the seaside town of Cambrils. Seven people were hurt and five attackers were killed by police.
Authorities this morning said they believe a cell of eight people may have been involved in planning both attacks, and wanted to use gas cannisters as weapons.
Overnight in Barcelona, an eerie silence pervaded the centre of a city that would usually be bustling until the early hours at the height of the holidays.
Some tourists dressed in shorts and t-shirts stood behind security tape close to the scene.
A text message spread from phone to phone with a warning not to share photos of the attack.