Rio de Janeiro (CNN) Sirens blaring, an ambulance peels out of the parking bay of a firehouse in southern Rio de Janeiro -- our car in hot pursuit.

We've been given access to Rio's First Emergency Response Battalion for the day, to see how prepared they are for medical emergencies during the upcoming Olympic Games.

We speed through crowded streets for some time, but then traffic strikes. We're stalled.

I check my watch. It's been 18 minutes since we left -- response time in most major cities in America is about nine minutes

A couple of minutes later we arrive. But no, actually, we're lost. We've stopped because paramedics aren't completely sure where the patient is. Better directions are called in from dispatch and finally, success. It took 25 minutes from start to finish.

The victim, one of Rio's many homeless, is passed out on the street. "Did he fall?" the medics ask a woman standing nearby. "No, he just laid down and passed out," she replies.

Quickly, his head is padded and he's strapped onto a stretcher and wheeled over to the ambulance. There, medics attempt to revive him, doing all they can to avoid a trip to the hospital. This is one of the many ways Rio tries to ease the burden on overcrowded medical centers.

Emergency room in a public hospital dedicated to Olympic visitors.

I soon see why.

"So these pictures show pretty much the five hospitals that they have dedicated for the Olympics. They have patients in the hallways. They have patients lying on the floor sometimes. It's a completely crazy situation," says Nelson Nahon, a doctor for Rio's regional Council for Medicine, a medical watchdog association called CREMERJ.

The pictures Nahon is showing me are startling. They remind me of makeshift medical shelters put in place after natural disasters. Patients on gurneys are shoved into every spare corner, lined up like dominoes.

Doctors must move one patient's bed to treat another.

"This is a picture of the red room -- the emergency patients," he says, gesturing to images CREMERJ has captured to illustrate the problem. "You can see the beds crammed next to each other, in row after row. So when the doctors walk in to see a patient, they have to put a bed aside, then put another bed aside, so that they can actually reach the patient."

A black body bag lies next to patients waiting for treatment.

Most disturbing is the site of a body bag lying in a bed next to other patients, waiting to be removed.

"This is a completely absurd situation, where a patient died and they put him inside this black bag next to others," says Nahon. "Normal procedure would be to take the deceased patient outside and then put him in the black bag and then forward him to wherever he should go."

Nahon tells me this type of overcrowding is common among Rio's public hospitals.

"Every day in Rio, we lack about 150 beds for emergency care," he says. "Intensive care is the same. They might even die in that period because they need intensive treatment and in the semi-intensive rooms they have, people who are supposed to stay there for 24 hours -- they stay for 15 days."

Elective surgeries and cancer treatments are delayed by weeks.

This doesn't even count the people who are waiting for elective surgery, such as "cancer treatment or amputation due to diabetes." But as bad as all this is, it's not what keeps Nahon up at night.

"My main concern is that if we have a terrorist attack and there are multiple patients," he says with a frown. "Because our emergency rooms are not empty waiting for people. They are still running, still receiving people every day."

A startling contrast

When I step into the Americas Medical City Hospital , it's hard to imagine that I'm in the same country. The chaos of people desperate for care has been replaced with the busy, but quiet, hum of a hospital that I'm used to. It feels like a big city academic hospital back in the United States.

For the next few weeks, this hospital will be under the watch of Dr. Antonio Marttos, a trauma surgeon from the University of Miami.

Americas Medical City will receive athlete patients coming from the Olympic Village.

A Brazilian native, Dr. Marttos has spent most of the past three years commuting back and forth from his home in Miami to ready the facility for the 2016 Olympic Games. He has been tasked with overseeing all trauma and emergency services during the Games. This includes the Olympic Village Polyclinic -- a mini hospital in the Olympic Village that provides everything from emergency services to dental care -- as well as the Americas Medical City facility, which is composed of two hospitals, one that will cater to athletes and the other to Olympic dignitaries and VIPs.

If someone needs to be rushed from the Olympic Village or the Polyclinic to the hospital, it should take approximately 12 minutes.

It's full-service healthcare that will be run by a staff of 5,000 doctors, nurses, and other medical personnel -- many of whom will volunteer to do these jobs.

While many of the larger countries taking part in the Games come with their own medical teams, many smaller countries use this as an opportunity to get basic check-ups and preventative care.

Dr. Marttos tells me that in the event of an injury, a doctor needs to be on hand right away. "My role is to be sure my hospital has everything in place. We have protocols and guidelines," he said. "It looks like an American hospital, they have everything ready, like my hospital in Miami."

As a reporter, I've been talking a lot about Zika, Rio's notoriously dirty water and even threats of terrorism. When I ask him how much of a concern this is for him, he says his priority is the athletes. "How to take care of the injuries. Everything else, terrorism, is not under our control. Brazil got ready. They did a lot of training."

He adds, "I can say that for all the athletes, for all the people inside the venues, if they need us, we're going to be ready to take care of them."

Waiting times in public hospitals won't improve during the Olympics.

As we tour the nearly 500-bed hospital, I can't help but think of just how starkly different this facility is compared to the pictures of the public hospitals that Dr. Nahon showed me: rooms filled to capacity, patients waiting for days for emergency services -- sometimes dying before being treated -- and the body bag next to a patient.

I ask Dr. Marttos what he thinks of the public hospital situation. He's very diplomatic and says that sometimes the physical infrastructure isn't the same as here. The walls may not be as nice, the equipment not quite as new, but that the quality of the doctors is the same.

He's optimistic that perhaps the work that he has put into the facility here will be a legacy for the care for future Brazilians.

More people turning to public hospitals

I'm back in the command center for Rio's Emergency Response Battalion, feeling the pulse of activity. More than a thousand people help keep the ambulances running and responding to emergencies 24 hours a day. The control board fills an entire wall, tracking minor to major injuries with color codes of blue, yellow and red.

Doctors, both military and civilian, triage the calls, making sure that everyone who gets an ambulance truly needs one. They cannot afford to waste efforts, especially with the extra stress of the Olympics.

Lt. Col. Carlos Sima shows me around his command center with pride, and puts a good face on their lackluster response time and the well-known overcrowding of the hospitals they deliver to.

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"The economic crisis has made it very difficult," he tells me. "Even people who used to afford private hospitals are now going to public ones to save money."

I ask him what his biggest concern is during the upcoming Olympics, and hear a familiar refrain.

"A terrorist attack," he says quickly. "We don't have history with that. We are used to big accidents and the like, but because we don't have a history with terror, that would be of real concern."