“I don’t even know if my child is alive or dead,” he said, as his wife began weeping. Relatives had been sent photos on their phones showing the son lying in a pool of blood, but shielded the parents from the images. The relatives also had a video showing Mr. Daitzik’s daughter, wearing a red T-shirt, running and screaming, having ducked the gunfire. A few minutes later, the daughter arrived at a hospital in an ambulance, traumatized.

Chancellor Angela Merkel will convene a meeting of her security cabinet on Saturday. “It is terrible and completely unbelievable what has happened in Munich,” Interior Minister Thomas de Maizière said as he cut short a trip to the United States to return to Berlin.

In Washington, President Obama expressed support for Germany. “We don’t yet know exactly what’s happening there, but obviously our hearts go out to those who may have been injured,” he said from the Eisenhower Executive Office Building. “It’s still an active situation, and Germany is one of our closest allies, and so we are going to pledge all of the support that they may need in dealing with these circumstances.”

Mr. Obama was briefed on the situation by Lisa O. Monaco, his assistant for homeland security and counterterrorism.

The German foreign minister, Frank-Walter Steinmeier, said Friday night: “We are following the news from Munich with horror. What is behind this hideous act is not completely clear; we still have conflicting leads. But already this much is clear: We will have to mourn for many fatalities and injured.”

The police sent out text messages warning people to stay in their homes and to get off the streets. The mall itself took several hours to evacuate. A square in central Munich, the Karlsplatz, also known as the Stachus, was evacuated after reports of gunfire, which appeared to have been a false alarm.

Passengers who landed at Munich Airport on Friday evening found themselves stranded on the curb outside. The taxi line stretched at least 40 people deep, and airport officials said that the highways leading into the city had either been closed or been subjected to tight police checkpoints.

Manfred Reiter, 47, a taxi driver, said he had received a call from his company’s dispatcher telling him to avoid picking up customers from the street because the attackers were on the run and might try to flag a cab. “He said, ‘Manfred please go home; it’s too dangerous,’ ” Mr. Reiter said.

Miriam Arlt, who was in the area, said in an email interview that she was near the McDonald’s when the shooting occurred.

“I only saw fleeing people and now see police and a helicopter,” she said.

Her roommate — who asked to be identified only as Hendrik A. because he felt traumatized by what he had witnessed — said by telephone that he had been riding his bike toward the McDonald’s when he came upon the site of the attack.

“I was over at the shopping center waiting for the light to get to McDonald’s,” he said. “I didn’t even realize the chaos or the panic that was around me. I came to a stop light, and then I first realized that things were not normal. There were three bodies lying on the ground. And my first thought was ‘O.K., they’re just lying on the ground; nothing really happened.’ Two of them didn’t move. One did.”

Then he heard gunfire erupt behind him — “five to eight shots” — coming from inside the shopping center. People started to run, he said. “It was not insane panic like you would imagine, a stampede or anything, but people were a little uneasy.”