Just before 6 p.m., the van jumped the curb and began speeding down the pedestrian walkway at the center of Barcelona’s most famous street. Witnesses said the driver appeared to be weaving to hit as many people as he could.

The attack began near Plaza de Cataluña. Photographs and videos showed people crying and running for their lives. Emergency crews rushed to help victims lying on the ground. The images bore a grim resemblance to recent vehicle attacks carried out in France, Germany, Sweden and Britain.

The van continued for more than 1,600 feet, or about half a kilometer, leaving a trail of wounded people, debris and smashed kiosks.

Officials said 13 people were killed and at least 100 were injured.

Eyewitnesses reported that children were among the victims. Two strollers were seen abandoned along the path. A video posted online showed a man lying beside another stroller, with children crying next to him.

The van came to a halt on top of a tile mosaic by the Spanish artist Joan Miró. A video posted on Facebook showed at least 15 people lying on the ground in the last hundred feet before the van stopped.