TEL AVIV -- As Jennifer Damti sat between her two daughters in her Tel Aviv home Sunday, she was unable to hold back tears, saying she is worried sick that her youngest child was taken hostage in the surprise attack launched by Hamas militants.

Damti told ABC News her 22-year-old daughter, Kim, whom she described as having big green eyes and a huge smile, is missing, possibly one of a large crowd of desert partygoers set upon by armed men in vans and wearing balaclavas.

She said she last heard from her daughter in a phone call Saturday at 6:30 a.m. local time just as Hamas militants launched a surprise attack on Israel, indiscriminately firing thousands of missiles from Gaza into southern and central Israel, including Tel Aviv. Damti said as the militant moved in on the party Kim was attending, her daughter asked, "Mummy, what should I do?"

Damti said her son took the phone and told his sister to find shelter. Since then, they haven't heard from her.

As the missile attack was commencing, Hamas militants on motorcycles and in vehicles stormed blockaded areas of Gaza and infiltrated Israel, officials in Israel said.

Video footage emerged of Hamas terrorists shooting Israelis and taking others hostage.

The Israeli government confirmed that a number of civilians and soldiers have been taken hostage. At least 100 Israeli citizens and soldiers are being held hostage by Hamas fighters, Israel's Government Press Office said Sunday.

U.S. Secretary of State Antony Blinken said the Biden administration is trying to confirm reports that Americans are among those killed or taken captive.

As of Sunday afternoon, at least 700 people had been killed in Israel by Hamas and another 2,100 have been injured, the Israeli Health Ministry said. Israeli rescue service Zaka said at least 260 bodies were removed from the venue of the music festival in southern Israel that came under a Hamas attack.

The Palestinian Health Ministry said 370 are dead and 2,200 others are injured in Gaza in retaliatory strikes by Israeli jet fighters and soldiers.

Israeli Prime Minister has declared "Israel is at war."

"Kim didn’t realize seven or eight Toyota vans (were) full of terrorists,” Damti, crying, said of her daughter. "They just shot everywhere. They slaughtered them like ducks. This behavior is barbaric. I didn’t bring my children up to hate anybody. I’m asking the world to condemn this."

Damti said the family hasn’t slept since the onset of the attack as they wait by the phone for word on her daughter's fate.

She said her daughter's father and brother have been traveling from hospital to hospital with a hairbrush containing Kim's hair, hoping for a DNA match and some answers.

Damti showed ABC News a photo of her missing daughter, pointing out her unique curly blond hair.

"I know my daughter, she’s a gentle loving person, who wants to make the world a better place. I don’t know if we’ll get her back," Damti said.

The thought of never seeing her daughter again prompted more tears and fears that the worst had befallen her girl.

"Maybe she’s been taken as a hostage in Gaza. I don’t want to think about that. Maybe she’s hiding somewhere. She’s clever. Or maybe -- I don’t know... I don’t even want to think." she said.

Damti's other daughter, Emily, said the family has also been combing through online videos of kidnappings and killings they said were carried out by Hamas militants, looking for any sign of her sister. But Emily said their search has yet to produce "nothing.".

“You can’t sleep. All I can think about is where she is," Damti said. "If she’s suffering, if she’s still alive. I just want her back. I have three daughters. I can’t imagine my life without Kim."

ABC News' Bill Hutchinson contributed to this report.