France declared a state of emergency and secured its borders Friday night after attackers unleashed a coordinated wave of explosions, gunfire and hostage-taking in Paris that left more than 120 people dead and generated scenes of horror and carnage.

Taken together, the assaults represented the deadliest day of attacks in France since World War II and one of the worst terrorist strikes on Western soil since Sept. 11, 2001. At half a dozen sites across Paris — a soccer stadium, restaurants, a concert hall — the attackers carried out suicide bombings, hurled grenades and shot hostages dead in a frenzy of violence that paralyzed the city. Late into the night and early Saturday morning, heavily armed security forces flooded the streets while panicked residents and tourists sought safety indoors.

Friday was the second time this year that the City of Light has been a scene of mass murder; in January, Islamist gunmen attacked the satirical newspaper Charlie Hebdo and a kosher supermarket, leaving a total of 17 dead.

The latest violence will only heighten the tension on a continent that is already on edge from the accumulated strain of a historic migration crisis, growing Islamist extremism and increasingly polarized politics.

President Obama expressed his condolences and offered his assistance to France after simultaneous attacks around Paris on Nov. 13, 2015. (Reuters)

World leaders rushed to condemn the attacks, and French President François Hollande vowed revenge, though there was no immediate claim of responsibility. “We are going to lead a war which will be pitiless,” Hollande said outside the Bataclan concert hall, scene of the most bloodshed.

“Because when terrorists are capable of committing such atrocities, they must be certain that they are facing a determined France, a united France, a France that is together and does not let itself be moved, even if today we express infinite sorrow.”

The violence was quickly celebrated online by backers of the Islamic State and other extremist groups. The scale and sophistication of the attacks will be likely to prompt questions about how the planning for such an operation evaded the scrutiny of French intelligence services.

Until the early hours of Saturday morning, some of the gunmen were thought to remain at large. But the Paris prosecutor’s office announced Saturday that all eight of the attackers had been killed — seven of them by detonating explosives.

Still, authorities warned that accomplices could remain at large. "To plan six attacks you need a lot of people involved, not only those who were at the spot," said a senior European counter-terrorism official, who spoke on the condition of anonymity.

The killers traced an arc across the city, targeting lightly secured facilities where tourists and residents had been enjoying the sort of experiences and events that define Friday night in Paris on a cool November evening. Soccer games, concerts and evening meals were all violently disrupted by the sounds of explosions and gunfire.

The scene of the worst carnage was the 19th-century Bataclan concert hall, one of the city’s most famous music venues, where hundreds of people had gathered for a show by an American band, Eagles of Death Metal.

What we know so far about who carried out the Paris attacks

As attacks reverberated elsewhere in the city, gunmen stormed the building. Witnesses said three or four men, clad in black, used assault rifles to mow down audience members, shooting some as they dove to the floor seeking safety.

“There are survivors inside,” a man named Benjamin Cazenoves posted on his Facebook account, saying he was in the hall before police closed in. “They are cutting down everyone. One by one.”

Police surrounded the building and, amid the boom of explosions and rattle of gunfire, moved in. As they did so, the attackers blew themselves up with explosive belts, police said. Inside, officers found evidence of a massacre, with at least 118 people dead, the city’s deputy mayor, Patrick Klugman, told CNN.

Government personnel guided survivors of the attack, wrapped in gold-colored heat blankets, down the street to waiting buses. Several had blood spattered on their clothing. Some cried. Most declined to talk to reporters.

One middle-aged woman with brown curly hair and wearing a white sweater called out from the group of survivors to a man on the other side of a police barrier. He rushed over, embraced her, and the pair simply stood, locked in each others’ arms, for several minutes.

At other sites across the city, attacks left dozens more dead. There were conflicting reports of the exact numbers.

Outside a popular cafe, witnesses reported seeing piles of bodies in the street, the cafe windows having been riddled with gunfire.

At the soccer match, terrified fans gathered on the field, having been barred by authorities from leaving ­after suicide bombers detonated explosives outside the stadium just north of Paris. The blasts near the stadium prompted authorities to evacuate Hollande, who was among thousands watching a friendly match between France and Germany.

Across Paris, normal city life came to a halt. Subway lines were shut down, and authorities advised residents to stay indoors. People who had been on the street in areas near the attacks fled in a panic.

“I was outside smoking a cigarette when I saw some people coming towards us saying an attack was going on at the Bataclan,” said Charlotte Baudoin, a 29-year-old event manager. “So everybody ran back inside the restaurant and they locked the doors. We stayed inside for 50 minutes with the lights off. Then they told us to leave, but we did not feel safe on the streets.”

Hollande went on national television Friday night to announce a state of emergency, including restrictions at French borders and the deployment of the army. The president’s office said 1,500 French troops would hit the streets of Paris to back up police.

The border controls came amid growing signs across Europe that the continent’s tradition of free movement is at grave risk. Despite rules for passport-free travel, Sweden instituted border checks this week to better control an unprecedented flow of migrants from the Middle East, southern Asia and Africa. Slovenia rolled out razor wire on its border with Croatia.

While the new French border controls were expected to be strict, international airlines and trains appeared to still be operating.

In Washington, a somber President Obama appeared in the White House briefing room to offer condolences and U.S. help “to bring these terrorists to justice.”

He said the wave of violence was not just an assault on France but “an attack on all of humanity and the universal values we share.”

Obama, who is scheduled to leave Saturday for the Group of 20 summit in Turkey, said he spoke prior to the attacks with Hollande .

“All of Paris needs our prayers tonight,” House Speaker Paul D. Ryan (R-Wis.) tweeted.

German Chancellor Angela Merkel on Saturday delivered sobering remarks about the attacks. “Behind us lies one of the most horrible nights Europe has experienced in a long time,” she said.

Within minutes of the first reports on the violence, Islamic State supporters created hashtags hailing “Paris in flames” and declaring that “ISIS is attacking Paris,” the Vocativ Web site reported. (ISIS is another name for the Islamic State.)

Mary Lou Dorio, the mother of Julian Dorio, the drummer for Eagles of Death Metal, said in an interview that her son and other band members managed to escape the concert hall when the attack there began. However, the fate of several crew members remains unknown, she said.

“It was awful,” she said. She added that her son was at a local police station, where he was able to call his wife.

“It was a bloodbath,” Julien Pearce, a radio reporter in France, said in an interview with CNN. He said he was at the concert and saw three or four young men dressed in black open fire on the crowd with assault rifles, firing at random as people screamed.

“They didn’t shout anything. They didn’t say anything,” he said of the assailants. “They were just shooting people.”

Witte reported from London. Karla Adam in London, Cléophée Demoustier and Ryan Weber in Paris and Greg Jaffe, Adam Goldman and William Branigin in Washington contributed to this report.