BERLIN — A truck rammed into a crowded Christmas market in central Berlin on Monday evening, killing 12 people and injuring nearly 50 as it smashed through tables and wooden stands.

The popular Christmas market outside the Kaiser Wilhelm Memorial Church was filled with a mix of tourists and locals when the large Scania truck hurtled into it. Germany’s top security official said initial evidence pointed to an intentional act, and the White House condemned “what appears to have been a terrorist attack.”

Police said early Tuesday that 48 people were in hospitals, some of them with serious injuries.

Mike Fox, visiting from Birmingham, England, told The Associated Press that the truck missed him by about three meters. Fox said he helped people who appeared to have broken limbs, and that others were trapped under Christmas stands.

“You do what you can to help who you can, really. It happened so fast that there was nothing we could do to stop it — if we’d tried to stop it we would have been crushed,” Fox said.

The truck, which was loaded with steel beams, came to a halt on a sidewalk on one side of the market. It had just rammed a large stand called “Fascination Christmas,” tearing off one side and knocking down a large Christmas tree. The three-meter tree lay in the street, red and gold ornamental balls still attached to its limbs and a golden star at the top.

A suspect in the truck attack, who was arrested Monday night and denies involvement, came from Pakistan and registered as an asylum-seeker in Germany last year. Merkel said it would be “particularly sickening” if the assailant were confirmed to be an asylum-seeker — both for Germans who help refugees and “for the many people who really need our help and are making an effort to integrate in our country.”

The crash came less than a month after the U.S. State Department called for caution in markets and other public places across Europe, saying extremist groups including Islamic State and al-Qaida were focusing “on the upcoming holiday season and associated events.”

The Islamic State group and al-Qaida have both called on followers to use trucks in particular to attack crowds. On July 14, a truck plowed into Bastille Day revelers in the southern French city of Nice, killing 86 people. Islamic State claimed responsibility for that attack, which was carried out by a Tunisian living in France.