Images posted on social media appear to show people being tended to as they lay on the street.
Reports said the driver escaped the scene on foot and was holed up in a bar in Tallers Street. Armed police ran down the streets and through a market, checking in stores and cafes.
In photographs and videos, at least five people could be seen lying on the ground in the streets of the northern Spanish city on Thursday afternoon, being helped by police and others. Other video recorded people screaming as they fled the van.
Carol Augustin, a manager at La Palau Moja, an 18th-century place on Las Ramblas that houses government offices and a tourism information center, said the van passed right in front of the building.
“We saw everything. People started screaming and running into the office. It was such a chaotic situation. There were families with children. The police made us close the doors and wait inside,” she said.
While full details of the incident were not immediately clear, since July 2016 vehicles have been used to ram into crowds in a series of militant attacks across Europe, killing well over 100 people in Nice, Berlin, London and Stockholm.