Shani Louk, a German-Israeli national, was among festivalgoers who had gathered in farmland near the Gaza-Israel border for what was supposed to be an all-night dance party celebrating the Jewish holiday of Sukkot.

Instead, in the early hours of Saturday morning, it was swarmed by Hamas fighters who gunned down revelers and took others hostage, as they launched an unprecedented assault on Israel.

Louk was later pictured in a video, identified by her dreadlocks and tattoos, being paraded through Gaza as onlookers shouted "Allahu Akbar."

She is among a large number of Israeli nationals who have been taken hostage by Hamas militants and are now being held in locations across Gaza, complicating Israel's response to the deadly attack.

Israel is taking pains to establish the exact number of hostages that have been taken into Gaza, an isolated coastal enclave of almost 2 million people crammed into 140 square miles, one of the most densely populated places in the world.

Lt. Col. Richard Hecht, the military's international spokesperson, told CNN on Sunday that "dozens" had been captured and emphasized just how complex the situation was as the army launched air strikes on Gaza in retaliation. In an earlier briefing he had said "civilians, children and grandmothers" were among those being held captive.

Hamas claims it has captured dozens of Israelis, including soldiers, and videos authenticated by CNN show some of the dramatic seizures.

Al Qassam Brigades, the armed wing of Hamas, has warned attacks in the area could impact hostages, with its spokesman, Abu Obaida, saying in a recorded audio message Saturday that they were "present in all axes in the Gaza Strip."

Lt. Col. Jonathan Conricus, an Israel Defense Forces (IDF) spokesperson, told CNN's Wolf Blitzer that "it is unprecedented in our history that we have so many Israeli nationals in the hands of a terrorist organization."

It has been more than 17 years since an Israeli soldier was taken as a prisoner of war in an assault on Israeli territory. And Israel has not seen this kind of infiltration of military bases, towns and kibbutzim since town-by-town fighting in the 1948 war of independence.

Here's what we know about some of the Israeli hostages taken by Hamas.

Music festival

Hundreds of attendees at the Nova music festival ran across the plains of the Negev Desert near Urim, a community close to the Gaza Strip, trying to escape Hamas gunmen pursuing them in vehicles in a terrifying chase. Some were killed and others were seized by armed captors, social media videos showed.

Details of hostages from the attack are beginning to emerge as family members recognize relatives in the clips circulating online.

In one video that went viral, an Israeli woman and her boyfriend -- identified as Noa Argamani and Avinatan Or -- were shown being kidnapped. In it, Argamani was hoisted onto the back of a motorcycle and driven away as Or was apprehended and made to walk with his hands behind his back. CNN could not independently verify the video.

"It's very difficult when you see someone that is so close to you and you know so much being treated like this," Amir Moadi, a roommate of Noa Argamani, told CNN, adding that he knew about five or six people who had been at the festival and have since gone missing.

In another video authenticated by CNN, an unconscious woman who was at the festival could be seen being displayed by armed militants in Gaza. CNN later confirmed the identity of the woman as Louk. CNN has reached out to her family for comment but has not yet received a response.

Her cousin confirmed to the Washington Post that Louk attended the music festival.

CNN does not know Louk's whereabouts or condition at this time. CNN is not airing the video because it is graphic and disturbing.

"We recognized her by the tattoos, and she has long dreadlocks," Louk's cousin told the Washington Post. "We have some kind of hope... Hamas is responsible for her and the others."

Israeli border communities

Hamas fighters took hostages in the border community Be'eri, and the town of Ofakim, 20 miles east of Gaza, IDF spokesman Brig. Gen. Daniel Hagari said on Saturday, adding that the two locations were the "main focal points" of the unfolding crisis.

In a televised address, he said that there were special forces with senior commanders in the two communities, and fighting was ongoing in 22 locations.

One video, geolocated by CNN to Be'eri, appears to show Hamas militants taking multiple Israelis captive.

Residents in Be'eri and another community on Israel's border with Gaza, Nir Oz, told the country's Channel 12 television station that assailants were going door to door, trying to break into their homes.

Channel 12 also reported that infiltrators had taken hostages in Netiv HaAsara. Israeli authorities did not immediately confirm any details about those reports.

One Israeli mother told CNN she had been on the phone with her children, aged 16 and 12, who were home alone when they heard gunshots outside and people trying to enter. Then, over the phone, she heard the door break down.

"I heard terrorists speaking in Arabic to my teenagers. And the youngest saying to them 'I'm too young to go,'" the mother said. "And the phone went off, the line went off. That was the last time I heard from them." CNN is not identifying the mother and her children for safety reasons.

Another Israeli father told CNN he suspects his wife and young daughters may have been abducted while visiting Nir Oz. He said he recognized his wife in a viral video that shows a group of people being loaded on the back of a truck flanked by Hamas militants, while chants of "Allahu Akbar" ring out.

"I don't even know what the situation is regarding the hostages, and the situation is not looking good," Yoni Asher said, adding that he tracked his wife's phone and learned that it was located in Gaza.

In another video, geolocated by CNN to Gaza's Shejaiya neighborhood, a barefoot woman is pulled from the trunk of a Jeep by a gunman and then forced into the backseat of the car. Her face is bleeding, and her wrists appear to be cable-tied behind her back. The jeep also appears to have an IDF license plate, suggesting it may have been stolen and brought into Gaza.

Soldiers

Al Qassam Brigades claimed to capture "dozens" of Israeli soldiers on Saturday.

"We bring good news to our (Palestinian) prisoners and our people that the al Qassam Brigades have dozens of captured (Israeli) officers and soldiers in their hands," the group's spokesman Abu Obaida said in a post on Telegram. "They have been secured in safe places and resistance tunnels."

Video geolocated and authenticated by CNN shows at least one Israeli soldier being taken prisoner.

The video, posted to Hamas' official social media accounts, shows militants yank two clearly terrified and stunned soldiers out of a disabled tank. It's unclear from the video how the tank was disabled, but Hamas has used drones to drop bombs onto Israeli tanks before.

One of the soldiers is then seen in a short snippet of video being kicked on the ground by the militants. In the next clip, the soldier is seen lying motionless on the ground.

The second soldier is seen being led away by Hamas militants. A third soldier -- his face very bloody -- is seen lying on the ground motionless near the tank track. CNN does not know the current whereabouts or status of the three soldiers.

A second video, taken afterward, shows a number of different armed men around the tank. The three soldiers are nowhere to be seen.

The armed men are then seen pulling a fourth Israeli soldier from the tank. The soldier is motionless as he's dragged down the side of the tank and onto the ground. The armed men are seen stomping on his body.