An overnight manhunt for the attacker who killed a woman and injured 29 others at a Berlin gay Pride celebration stretched through Sunday afternoon with no resolution in sight, as government officials sought the public’s help in apprehending the man responsible for what they called an Islamist terrorist attack.

“These criminals, these extremists, have no place in the middle of our society,” Chancellor Friedrich Merz of Germany said on Sunday afternoon before entering a memorial service at St. Mary’s Church in central Berlin. “And we will not allow this poison of terrorism and this poison against our freedom to spread further.”

Kai Wegner, the mayor of Berlin, told reporters at a news conference near the site of the attack on Sunday afternoon that “we are presumably looking at an Islamist terror attack directed at our way of life, our liberal democracy, our openness and our freedom.”

Alexander Dobrindt, the federal interior minister, echoed that assessment, saying the attack was most likely Islamist terrorism. He said at the news conference that the main suspect was born in Germany and is a German citizen — with family roots in Lebanon — who had attacked people just outside the celebration with a rented van and a bladed weapon.

He said the suspect had a history of radicalization and a criminal record, including a conviction at an unspecified time for which the suspect had recently received a suspended sentence. The police said the suspect was known to them and was associated with what they called “the Islamist spectrum.”

Police and other officials said there could be more than one attacker involved. Mr. Dobrindt said a widespread search was underway across the city and throughout Germany, including at airports, rail stations and border crossings.

Early Sunday morning, the police released a photograph and a partial name of the prime suspected attacker, in an appeal for public help in locating the man, Abdul B., 21. His full surname was withheld under German privacy laws.

Berlin police first said early Sunday that they were searching for “at least one suspect” after the attack on the periphery of the annual Christopher Street Day parade, which drew hundreds of thousands of revelers to the city center on Saturday. The festivities included a concert on Saturday evening near the Brandenburg Gate and the Tiergarten, the city’s large central park.

Shortly after 10 p.m., the authorities said, a white minivan sped through a side street leading out of the park, outside of the official festival grounds and security complex, striking pedestrians on a sidewalk and eventually crashing into a tree. The driver ran away. Video footage showed the car’s front grille smashed and its body heavily dented.

Mr. Dobrindt said that some of the 29 people injured were hurt critically. He said the attacker had wielded what appeared to be a machete as part of his rampage. Some victims had suffered stab wounds. Emergency workers quickly arrived and began administering first aid, he said.

“It was a horrific scene,” Mr. Dobrindt said.

Berlin’s Charité hospital treated eight of the injured and had released four of them by midday Sunday, with the other four remaining in intensive care with non-life-threatening injuries, hospital representatives said on the social media platform X.

Mr. Dobrindt and Mr. Wegner did not take questions from reporters. They did not say if the man had links to any foreign actors or known terrorist groups.

In recent months, as the United States and Israel have engaged in war against Iran, German intelligence officials have privately warned of the threat of Tehran-sponsored attacks on German soil.

The attack abruptly ended a celebration that drew hundreds of thousands of revelers to Berlin, with organizers canceling a final slate of planned events on Sunday morning.

It rattled a community that had spent much of the day dancing in colorful costumes under idyllic summer skies.

It also immediately reignited a debate in Germany about migration, religious extremism and public safety. It came months before Berlin and two other eastern states are set to hold closely watched regional elections, where polls already have suggested far-right parties are poised to make gains, partly on the basis of Germans’ anxieties over public violence.

The event, named for the New York City street known for its association with the Stonewall riots that sparked the modern gay rights movement, draws hundreds of thousands of people to Berlin each year.

Early Sunday, roads near the site of the attack were blocked off by a heavy police presence. Nearby, emergency personnel had erected a tent to take care of distraught witnesses. Some were seen hugging each other, and some had thermal blankets wrapped around them.

Hours earlier, barricades had blocked vehicle traffic on roads leading through the Tiergarten, while throngs of revelers, many wearing glittery, colorful outfits, danced to the throbbing sounds of techno music, spilling into cafes and beer gardens nearby.

By late evening, the sounds of celebration had given way to the blare of sirens and the drone of helicopters circling over the area.

Alfonso Pantisano, the L.G.B.T.Q. affairs commissioner for Berlin’s state government, said in an interview on Sunday that he was in the crowd at the celebration when organizers announced an evacuation order immediately after the attack. He stayed to help others evacuate, he said.

Mr. Pantisano has helped lead an effort meant to respond to growing incidents of violence against Berlin’s L.B.G.T.Q. community. He said the attack “was a surprise, even though we were all thinking that at some point it would and could happen.”

“It could have been all of us” targeted by the attacker, he said. “And that is the scary thing about it.”

Philip Kaleta and Verena Hölzl contributed reporting.