Transcript for Manchester concert terror attack survivors describe chaos, helping others

Good evening. We are dedicating our entire show to the fast-moving developments out of England in the wake of the horrific attack on the Ariana grande concert. Children, teens, and families targeted. Tonight the British prime minister has put the entire country on its highest threat level warning another attack could be imminent. Meanwhile, we're learning much more about the suspect. We begin here tonight with ABC Terry Moran in Manchester, Terry? Reporter: Dan, tonight Manchester is quiet. It's been quiet all day. A great city subdued in shock and sorrow. About what happened right back there at the Manchester arena. The terror attack at the end of aria Ariana grande's concert. 22 dead, 59 injured, so many of the victims young people, teenagers, even children. We're learning more tonight about the 22-year-old british-born attacker and about those harrowing moments of carnage and courage and love. ??? Reporter: They came out on a school night to see their idol. Thousands of teenage girls packing the arena. Just minutes after pop diva Ariana grande finishes her encore, in a shower of pink balloons -- 10:33 P.M. The house lights come up. Then the sound of the bomb. Oh my god. . What's going on? Reporter: Panic. Oh my god! Reporter: Confusion. Those pink balloons popping as the audience stampedes for the exits. Girls clamber over railings, dropping into the crowd, desperate to escape. Of course I freaked out, began running. We had to climb over chairs, rilings to get out of doors that were locked, we had to force them open. Reporter: Carol Taylor was there with a friend and their children. It was just smoke and embers falling down from the roof and people were screaming. And we just ran. We ran and ran. Reporter: Bethany Keeling was right near the exit when the bomb went off. Saw like a flash. Like an explosion flash. I grabbed my friend's hand and we just ran. But we looked and we could see the bodies on the floor. Everybody around me just screamed. We just all ran. We didn't know what to do. We thought something might have gone off. Reporter: Victims lying where they'd fallen. The ground was streaked with blood. I thought we were going to die, it was horrendous. Reporter: Police believe british-born Salman abeddi, 22 years old, dead noted a suicide bomb here in the area connecting the massive arena to the nearby train station. It took the lives of 22 people, 12 of them children, injuring 59 more. The "Son" newspaper publishing Abedi's photo. Among the lives loves 18-year-old Georgina Callander, a student studying health and social care. This picture of her with 18 yawn that grande taken eight years ago. And this little girl died after being separated from her mother and teacher. Remembered as simply a beautiful little girl in everress aspect of the world loved by everyone. According to news reports her mother is critically injured and still in the hospital, she might not even know what happened to saffie. Devastating news to the family of 15-year-old Olivia Campbell, who just this evening was confirmed dead. Her uncle Steven hotson and her mother had been searching the last 24 hours. Olivia's mother Charlotte clutching a picture of her daughter. If anybody has seen her, please contact the police. Reporter: Earlier today making this plea. I'm going through hell. I can't even explain what I'm going through. I just -- I need my daughter home. I need to know where she is. A mother shouldn't have to do this. Reporter: Charlotte posting on Facebook just hours ago, rip my darling, precious, gorgeous girl, taken far, far too soon, go sing with the angels and keep smiling, mommy lov you so much. Among the horrow, heroism. I kept talking to her telling her, you're going to be okay, darling. Reporter: Parents Kim and Phil dicks sprang into action, saving a 14-year-old girl's life as they frantically searched for their own daughter and granddaughter. She was screaming out in pain. Her little arms and legs were all just broken, I ka tell. She was in so much pain, bleeding so bad. I couldn't believe it. I thought my girls were dead. Then I -- but I thought, I can't let this little girl die. Reporter: Kim cradles the girl for nearly an hour, applying pressure to her wounds. Even managing to contact her father and thankfully Kim's own family was safe and sound. All the time I was holding and trying to be brave, I said, I'm not going did leave you until your dad, until we find your daddy, until he comes. Reporter: Joe Gregory was in his car waiting to pick up his girlfriend. He sees the flash. Hears the bang. Then it hits him. No! Reporter: When the bomb went off, many parents were waiting outside to collect their kids after the show. For some of the youngsters, it was their first concert. Pick Hayward plunged into the fleeing crowd searching for his daughter Kaitlin. I was outside, just outside the venue itself, when we heard a massive bang. Inside you're thinking, what am I going to do, what am I going to do, what am I going to do? Then you've got to think, I'm going to find her. That moment when I was working my way out the steps of what am I going to find? In the back of your mind you're thinking the worst. Then you saw her? Oh, huge relief. Huge relief, huge relief. Almost like she'd been born again. As dad, you must know that moment, yeah? This is the best moment of my life. It was that all over again. Reporter: 60 ambulances screeched to the scene, specialized teams rushing in, transporting patients to area hospitals. Call an ambulance, quickly! They were able to stabilize patients at the scene and assure they received the right treatment at the scene before evacuation to the hospital. Reporter: Children as young as 8 still unaccounted for as authorities try to frantically reunite families. Among the missing, clowe Rutherford and Liam curry. Courtney Boyle and boyfriend Philip trap. Martin Hepp separated from his friends. And Wendy fall, who hasn't been seen since the concert. Many taking their search to social media, pleading with users to help find the people still unaccounted for. For some, the social media pleas are working. This tweet indicating, all of these people have been found, let's keep going. The uk is now raising their terror threat level to critical, warning that more attacks could be imminent. There is a possibility we cannot ignore that there is a wider group of individuals linked to this attack. Reporter: Manchester police, interpol, and uk law enforcement all in a frantic search to determine if the suspect had accomplices. Part of this response has seen us arrest a 23-year-old man in connection with the attack. Reporter: A neighbor filming today as armed security forces raided the suspect's modest brick home, armed with rifles and shields. Unconfirmed reports of a gentleman, mid to late 20s, being removed from the address quite quickly by armed officers. Reporter: In the midst of all this fear and loss, the humanity of the people in Manchester is on full display. Taxi drivers gave free rides to those trying to escape. Local businesses and residents offered a warm bed, a spot of tea. Ariana grande tweeted right after the concert, broken. From the bottom of my heart I am so, so sorry. I don't have words. Today grande landing back in the U.S., greeted by her family and boca raton, Florida. Around the world and at home, leaders condemning the heinous attacks. So many young, beautiful, innocent people living and enjoying their lives, murdered by evil losers in life. I won't call them monsters. Because they would like that term. Reporter: ISIS has claimed responsibility for this attack. Although they claim responsibility for virtually every attack, we have not verified yet the connection. Reporter: At home in the U.S., authorities are on high alert. They've beefed up security at vulnerable open venues ranging from sporting events to concerts. All around the world, signs of solidarity. The eiffel tower. The colosseum in Rome. Dark in honor of the lives lost. And here in Manchester, there's an unbreakable spirit as hundreds gather to honor the 22 killed. Whatever our religion, whatever our beliefs or our politics, we will stand together. Reporter: Not, not even terror, can shake their will to carry on. It's just sort of in our blood here. You just get on with it. Events in France and England, we've got to stand together and don't change. Because they want us to change, don't they? They want us to hide. They want us to stay in. To be frightened of going to concerts and soccer games. We're not going to do that. Reporter: For "Nightline," I'm Terry Moran in Manchester, England.

This transcript has been automatically generated and may not be 100% accurate.