Transcript for At least 19 dead at Ariana Grande concert in Manchester, England

Good evening. Thank you for joining us. Breaking news out of Manchester, England tonight. A deadly blast outside of an Ariana grande concert, killing at least 19, injuring at least 50. Police treating this as a terrorist incident. The leading theory? A suicide bomber. We turn now to ABC's chief foreign correspondent Terry Moran in London. Terry? Reporter: Byron, it was right at the end of the Ariana grande concert tonight in a stadium filled with her fans including so many teens and young girls and their moms. That's her fan base. When this huge explosion rocked not just the arena but the whole surrounding neighborhood. Felt blocks away. Arena officials saying that the explosion happened just outside the venue as people were coming and going. Eyewitnesses saw many dead and injured on the ground. Inside the lights went up, panic set in. People headed for the exits. They helped the wounded. They helped each other get out as law enforcement swarmed the scene and set up a perimeter. Hed parents took to social media looking for their loved ones. Tonight Manchester police are investigating this as a major terrorist incident and the city is on edge. Byron? Terry Moran, thank you. Tonight, eyewitnesses describing a scene of panic. A night that was supposed to be about music and fun. Reporter: That's the sound of the explosion that rocked Manchester erng Manchester, England tonight. Oh, my god. What just happened? What's going on? Oh, my god! Reporter: An unidentified blast outside the Manchester arena. Bringing bloodshed to an Ariana grande concert. 19 confirmed dead and around 50 injured. Many still missing. We heard this bang. A big flash and then a rush of air. And just thought what the hell is that? And all I could hear was screaming. People crying. Everyone was just running everywhere. It was complete madness. Take your time and keep exiting the building. Reporter: And tonight the city is shaken. Authorities are treating the event as "A terrorist incident." A U.S. Law enforcement official telling ABC news the leading theory, a suicide bomber. We are currently treating this as a terrorist incident until we have further information. Reporter: The mayor of Manchester saying this is a terrible night for our great city. And British prime minister Theresa may calling this "An appalling terrorist attack." There was a lot of screaming and a lot of parents trying to sort their families together. There's a lot of children there without parents. There was no one to calm them down. So everyone was just screaming and crying and pushing. It's shocking what happened. Just carnage everywhere. The ground shook. It was like bang, bang. Reporter: Panicked concertgoers sprinting to the exits after the boom. Authorities rushing to the scene. The cause of the explosion still remains unknown. An investigation is under way. We are working closely with national counterterrorism policing network and uk intelligence partners. This is clearly a very concerning time for everyone. Reporter: The concert began at 7:5:00 p7:35p.m. Local time. Part of the pop singer's dangerous woman arena tour. The crowded arena, one of the largest in Europe with over 20,000 seats, was packed near capacity according to witnesses. Ivo delgado Rivero was in attendance. Everything was going perfectly. And then the concert ends abruptly and then the lights came up and everyone started to go to the exits. Reporter: At around 10:33 P.M. After the concert had ended fans in the arena surrounded by pink balloons heard a loud noise. Ariana grande had left. The lights had come up. Everyone was just getting out of their seats and walking toward the stairs when awful a sudden this huge sound which sounded like an explosion went off. As I was waiting, an explosion went off and it threw me through the first set of doors, about 30 feet to the next set of doors. When I got up from the ground there was about 30 people scattered everywhere. Some of them looked dead. Then we hear a loud bang and everybody started running to the opposite direction. We opened the door going on the main corridor. It was full of smoke. So we were trying not to push. And everyone was trying really to protect the kids. Reporter: That police dash cam video capturing a faint flicker of light and a loud noise. You must take your time and keep exiting the building. There's no need to run. Take your time. Reporter: The P.A. Announcer trying to prevent a stampede. Reassuring the crowd to keep calm. Many in attendance children and teens. The chaos spilling into the streets of Manchester, just over 160 miles from London. Family and friends taking to Twitter posting dozens of photos, searching for missing loved ones. SHAWN Campbell says her 15-year-old daughter Olivia hasn't been heard from in hours. I don't know if she's going to walk back through the door or not. I feel sick to the bottom of my stomach. I love her so much, and I just want her home. Reporter: Local hotels reportedly taking in children separated from their chaperones. Several hours later police alerting those nearby of a potential secondary item and to stay clear as it was destroyed in a controlled explosion. Let me just tell you where we are. As we were saying before -- Reporter: Authorities later confirming it was abandoned clothing, not a suspicious item. Tonight just the latest incident to shake Europe. Manchester adding to the growing list of cities threatened by terrorism. The United Kingdom has been on high alert since last March, after the attack in London near the house of parliament. 52-year-old Khalid Massoud drove a car into pedestrians on a bridge before exiting and fatally stabbing a policeman. Four people were killed. Representatives for grande confirmed tonight that the singer was unharmed. Tonight she tweeted, "From the bottom of my heart, I am so so sorry. I don't have words." The support online reaching around the globe. The message, "Pray for Manchester." The investigation continues. Emergency services still working the scene as day breaks on this somber city. And for more we now turn to former New York City police commissioner ray Kelly and former national security official Richard Clark. Gentlemen, we've had these conversations too many times before. Where do you think law enforcement was focusing their attention at this hour? Oh, there's a lot of things they're focusing on. Obviously a suicide bomber. The bod yit of the bomber is going to give them an awful lot of information. A lost forensic work will be done, trying to collect information to see any signature on the bomb. Cameras. Cameras are ubiquitous these days. They'll be looking at cameras. Any informants that they have that might be able to give them real-time information. Any ongoing investigations that may or may not have evolved. This individual or someone close to him. Are there any fingerprints of who this might lead to do you think? Once they know who it was, they will check the cell phone, mobile phone records. They'll check the internet records. And they'll do a web. They'll go out to say who was his friend? Who was he talking to? Who was he talking to? The third and fourth level. And they'll try to find out is there an ongoing threat, is there an ongoing network that could do it again. A public place. Another soft target. But this seems different. This involved a concert where there were young girls. They were with their moms. Young families, teenage girls. This seems different to me. Maybe. Or it just might have been the venue that's in this city. It's a big 21,000 capacity stadium. So it just might have been a target of opportunity. But that will come out hopefully in the investigation as to why this target was picked. And what we saw here was you can take a venue and you can lock it down. You can pat everyone down. You can make everyone go through magnetometers. But just outside that perimeter there are going to be lots of PEOP people. And those people are a target. Does this point to ISIS, do you think? It is early on. You have investigative premises. And this is obviously something put into the equation. But you don't want to rule anything in or out at this juncture. But this is the kind of thing that ISIS teaches. Go for the soft target. Go for just outside the perimeter. Go for the individual.

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