Transcript for Hurricane-ravaged Puerto Rico facing 'unprecedented disaster'
What's out there is total devastation, total annihilation. People literally gasping for air. Reporter: It is the worst natural disaster to hit Puerto Rico in nearly 100 years. Hurricane MARIA pummelled the side last Wednesday. As a category 4 storm. We are many days removed from hurricane MARIA making landfall and you can see there are several neighborhoods that are flooded. Reporter: With basic supplies, food and drinking water running low and lines for gas, hours long. The 3.4 million American citizens in Puerto Rico are living on the edge. Everyone is fighting in the stores, in the streets, in the gas lines. It is really, really survival mode right now. If we don't get unprecedented collaboration from the federal government here, this could collapse into a humanitarian crisis. Reporter: This stunning image showing almost all of Puerto Rico blacked out. Most of the power you see, generators. No air conditioning. And the oppressive heat makes matters worse. At this sweltering 14-story retirement home in San Juan -- Door to door to door. There's no running water. The only way out, these stairs. What can I do? Here we meet this would that trying to care for her parents. Who desperately need medicine. They were just treated for dehydration. I wouldn't mind taking them to the hospital. They would be there. Reporter: Over the past week as Puerto ricans are pleading for help, trump faced criticism for tweeting about the NFL. Only reto Puerto Rico last night after five days of silence saying much of the side was destroyed with billions owed to Wall Street and the buildings which sadly must be dealt with, food, water and medical are top priorities and doing well. The irony of the fact that he criticized Puerto Rico for having Wall Street bailouts when he's been bankrupt five or six types and needed bailouts. That's not lost on people paying attention. Today she put the question to the president of. The Puerto Rico getting all the help it needs? They're fantastic people. I grew up in New York so I know many people from Puerto Rico. Reporter: The president highlighting the praise he's received. It is the most difficult job. It is on an island in the middle of the ocean. It is out in the ocean. You can't just drive trucks there from other states. The governor said we're doing a great job. Often he becomes self-congratulatory. That's not what people want. That's not reassuring. So it's been a challenge so far. The president said he plans to visit Puerto Rico next Tuesday. In the meantime, 12,000 employees are on the ground in Puerto Rico and the virgin Islands. The effort to bring supplies to those in need and rebuild critical infrastructure is a long it is particularal nightmare of the. As soon as we start bringing buses, something you're not even considering or taking for granted, then we can execute quicker. Today they brought in medical teams and additional generators. And since it made landfall, FEMA has provided 1.5 million gallons of water to the U.S. Virgin Islands and Puerto Rico with more help on the way. FEMA has been very responsive and sent an enormous amount of supplies very quickly. On the ground it's a race in type. Are you getting what you need fast enough? No, no. That's not politically correct to say. We are getting help and we appreciate it so much. You have no idea. The chain of command needs to work faster. For now Puerto Rico remains disconnected. Some like Jose are anxious to reconnect to family on the mainland. We loaned him our phone. I'm okay. She's worried about you. Yeah. Hundreds at the airport are still trying to get off the island. Flight navigation systems wiped out in the storm. I have high Blum and I'm not supposed to be -- it's not good. Tonight the only certainty is the long road ahead. This is the biggest catastroppe in Puerto Rico history. For "Nightline," San Juan, Puerto Rico.
This transcript has been automatically generated and may not be 100% accurate.