Transcript for Large fire engulfs high-rise building in London

breaking news. Flames engulfing a high-rise apartment building in London. We got word moments ago there are a number of fatalities. Witnesses said once the fire broke out it covered almost the entire tower within just an hour. That left anyone sleeping inside very little time to get out. We give you a live look. The smoldering building can be seen for several miles. A major concern at this minute, the building appears to be leaning to one side in danger of collapsing. ABC's Molly hunter is on the scene. Molly, what's the latest from your vantage point? Reporter: Good morning, kendis. That's right. You see the building right there still smoldering absolutely blackened but there are still flames up there. Down on the ground police are actually screaming get back but from where we are we feel that debris and can feel the spray from the firemen's hoses. A raging inferno high above London. Overnight incredible images flooding social media. Flames shooting from an apartment complex. Just like a waterfall on the left-hand side, a fire and flames but now spread to the right of the building, that part there. Reporter: The fire stretching 27 stories high. Flaming debris raining down on the streets below and ash covering everything for more than 100 yards away. This morning, witnesses saying there were signs of people trapped inside. Makeshift ropes seen hanging from the windows. British police pushing everyone away from the scene due to fears the building may collapse. This man saying he got out of the building after a neighbor banged on his door and woke him up. There was smoke everywhere. There was people downstairs. People screaming after a couple of minutes because people are still sleeping on the higher floors and they didn't have a clue of what was going on. I'm not even sure if half of them got out, and there were people flashing for help. Reporter: This morning as the sun rises the horrifying extent of the damage is visible. The building completely charred and still smoldering. Now, this is actually as close as we can get to that building. We're hearing bangs and creeks as if that building may actually collapse sometime soon. Kendis, Diane. Molly, I know not too long ago you could see someone still alive in the building waving at you. Is there any sense of when they'll be able to stabilize the building enough to try to get in there? Reporter: Diane, not any time soon. That's exactly right. We saw live video not from this vantage point of a man inside on the 11th floor. When you look at that, it's extraordinary to think that actually someone is still alive in there but police and the fire brigade are standing by waiting for any opportunity to rescue any survivors. We are hearing horrific stories of people jumping from the building. What are some of the other stories that you're hearing there? Reporter: Kendis, I think the thing that sticks out is the screams. So almost immediately as those flames -- the fire started below, the flames engulfed actually spread rapidly up to the top of the building and residents are talking about the screams of families, of children waving flashlights actually small children being tossed out of low floors to waiting arms below. The tragedy is absolutely unbelievable this morning. One of the big things we're hearing how quickly it spread, just an hour. Any sense of what caused this? Reporter: Diane, so what residents are telling us, a few things that may have caused that rapid spread and that may have also been the reason why so many people got trapped up above. So if that fire happened in your apartment or on your floor you were told to get out. But if the fire happened in a different part of the building, residents are saying they were told to actually stay in place. Now, they blame the rapid spread of flames on this external padding put in in a massive $13 million refurbishment. It was just refurbish the last year and external cladding put in in part for insulation and aesthetic reasons. As soon as that caught fire the entire building caught fire, this he say. Molly hunter on the scene of that horrific fire in the west of London. 128 units up in flames. There are some fatalities. Of course, we'll keep on top of this breaking news story throughout the morning.

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