“At this point, we believe there are three perpetrators, there are conflicting reports, but there are as many as three perpetrators on the run,” said Marcus da Gloria Martins, a spokesman for the Munich police. He said the suspects were armed with “long guns.”

At least one gunman opened fire near a shopping mall in Munich just before 6 p.m. on Friday, killing eight people and wounding scores of others in an assault that the German police said they were treating as a suspected terrorist attack.

The manhunt shut down traffic and public transportation across Munich, Germany’s third-most-populous city and the capital of the state of Bavaria. Police said they had found the body of a ninth person near the mall and were investigating the possibility that he was an attacker.

A state of emergency was declared in the city, plunging much of the metropolis into a desolate and fearful state of lockdown. As the transit system was shut down, commuters held their hands up in the air as they walked past police officers.

“At this point, we believe there are three perpetrators, there are conflicting reports, but there are as many as three perpetrators on the run,” said Marcus da Gloria Martins, a spokesman for the Munich police. He said the suspects were armed with “long guns.”

But a short while later, Peter Altmaier, the chief of staff for Chancellor Angela Merkel, said that security officials had specific information about only one individual, who was believed to be still at large. “We are certain about one person,” Mr. Altmaier said, adding that there was no information regarding the motive of the attack.

Police officers from Munich and from elsewhere in Bavaria flooded the city. An elite counterterrorism unit of the federal police has also been deployed to Munich, officials said.

The police issued an appeal to the public not to share images or photographs of the attack, of the victims, or of police operations, warning, “Don’t help the perpetrators!”

The police said they received a call around 5:50 p.m. Shots were reported from Hanauer Street, Ries Street and the Olympia-Einkaufszentrum, or Olympia Shopping Center, in the Moosach district, northwest of the city center, but it was not clear precisely where the shooting had occurred.

A video distributed online showed a man dressed in black opening fire near a McDonald’s restaurant that is next to the shopping mall.

Shooting victims began arriving on Friday evening at the Klinikum der Ludwig-Maximilians-Universität München, a university hospital, according to a spokesman there. The spokesman, Philipp Kressirer, said he did not yet have information about the conditions of the patients or how many were there. The hospital was one of several receiving and treating victims, he said.

Horst Seehofer, the premier of Bavaria, and Joachim Herrmann, the state’s interior minister, convened a crisis meeting at the State Chancellery in Munich.

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.”