An emergency room doctor calls it as "five-dollar insanity." A rehab director says it's the "devil's drug."

On the street, it's known as flakka — a synthetic crystal imported from China that is wreaking havoc in South Florida and threatening to spread its misery and profits across the country.

It's cheap, crazily addictive and terrifying. A single dose smoked, swallowed or snorted can give a user a potent but fleeting rush — or turn them into a paranoid zombie with superhuman strength and off-the-charts vital signs.

In the 14 months since the epidemic began in Broward County, 60 people have died. Hospitals are getting dozens of patients a day. And some nights, half the calls to police are flakka-related emergencies.

Broward Sheriff's Office Sgt. Ozzy Tianga and a deputy handcuff a man suspected of being under the influence of flakka so he can be transported to a hospital on June 17, 2015 in Pompano Beach, Fla. Joe Raedle / Getty Images

Homeland Security has a Florida unit devoted to the drug, and United Way of Broward County launched a multi-agency task force to crack down on the scourge.

"If we don't get it right here, it's going to explode," United Way chief executive Kathleen Cannon said.

Floridians say it's the worst drug crisis they have seen since the crack-cocaine epidemic of the 1980s. First responders describe nightmarish scenes with users running naked into traffic or impaling themselves on fences.

A 37-year-old old mother of two named Stephanie told NBC News about her first experience with flakka, which she unwittingly smoked during a drug binge.

A quick blast of euphoria was followed by a sickening fear. As the drug deregulated her autonomic nervous system, she began hallucinating that she was being chased and took off running.

Her body temperature spiked and she tore off some of her clothes and jumped three stories off a bridge into the Intercoastal Waterway.

"I just remember being in the water and feeling like I could breathe under water," she said.

Stephanie told NBC News she jumped off a bridge after her first experience with flakka. She is now in rehab. Courtesy of Stephanie

She still doesn't remember how she got out, but she ended up in the emergency room and then the psychiatric ward.

"I remember having seizures and having just continued paranoia and feeling like people were chasing me and following me and talking about me," she said. "And I still suffer from nightmares and have to take medication for that."

"It is by far worse than crack."

Stephanie is now in a drug-treatment program at J.C.'s Recovery House, where director Ray Rapaglia says 20 percent of his slots are taken up by flakka users, with many more turned away.

“We’re not as inclined to accept them in our program because we know that they might relapse," he explained.

“It's one of the most addictive drugs we’ve ever seen…and because it’s so inexpensive, for something like $5, addicts can get high for a couple of days. And then when they start to withdraw, they crave it. The body has an obsession for it."

"We're calling it the devil's drug," Rapaglia said. "I've never seen anything like it. It is by far worse than crack."

Robert Hutchinson, acting special agent in charge of Homeland Security Investigations in Miami, said nearly all flakka is manufactured in China, which only this fall classified it as a controlled substance that is illegal to export.

It's a cathinone, chemically related to drugs called bath salts, that goes by the pharmaceutical name of Alpha PVP. It can be ground into a powder and is sometimes used to cut other drugs because it's so inexpensive.

Flakka seized by the Department of Homeland Security. Department of Homeland Security

Displaying plastic bags from a recent seizure of seven kilos, Hutchinson said flakka can be bought overseas for $1,000 to $2,000 a kilogram, then sold to a U.S. wholesaler for $4,000 to $6,000 a kilo. Broken down on the street, that single kilo can fetch $40,000 to $50,000 in $5 doses.

"The profit margin is staggering," said Hutchinson.

“This is the Silicon Valley of drug smuggling right now. These are startups. These are people with a credit card and an Internet hookup.”

Investigators say college kids form one group of dealers. Hutchinson pointed to a student who was raking in $30,000 a week and driving a $100,000 Lamborghini, who is now serving a two-year prison sentence.

Traditional street gangs are also involved, with some hiring young children to serve as lookouts in exchange for a pair of sneakers, said Jim Hall, co-chair of the United Way's flakka team and an epidemiologist.

Because of the drug's low cost, the target customers are poor. NBC News accompanied police to Fort Lauderdale's main bus terminal where hand-to-hand deals were being done in open view.

“I talk to patrol and they say it’s every other call some nights…just one after the other, all flakka-related calls," said Capt. Dana Swisher of the Fort Lauderdale Police Department.

"Anytime we respond to a flakka-related call from patrol, we’re gonna require at last three to four officers to respond.”

Broward Sheriff's Office Sergeant Ozzy Tianga checks a woman's purse to see if she is carrying flakka on June 17, 2015 in Deerfield Beach, Fla. Joe Raedle / Getty Images

Capt. Mike Salzano of Fort Lauderdale Fire Department also sees the results of flakka abuse as he responds to calls for erratic behavior. During one run that NBC News joined him on, a woman wanted a man removed from her property.

"When you smoke that flakka, you start eating out the garbage cans and everything else," she told Salzano. "And then you gotta find a place to relax once you wear it off. And he end up in my yard early this morning, been here since almost 12 hours."

Every emergency worker seems to have a horror story. Swisher recalls the guy who tried to kick in a police station door. Several months ago, police got a report of a man swimming naked in the New River. He climbed up on a train bridge — which was probably 115 degrees in the hot morning sun — and rode it 150 feet in the air.

"We actually had to have fire rescue climb up there and basically tie him to the bridge with the firefighters so they could lower the bridge and take him off," Swisher said.

"This is the Silicon Valley of drug smuggling right now."

Dr. Nabil El Sanadi, chief executive of Broward Health and an ER doctor, said his hospitals first started seeing flakka patients in September 2014. Now they get 25 to 30 a day.

When they arrive, their heart rate is often between 150 and 200 beats per minute, with blood pressure at "near-lethal" levels like 230/160. They may have been injured struggling with rescue workers and sometimes their kidneys are already failing.

“They come in hot, crazy, insane, out of their mind and then on top of that, fast heart rate and high blood pressure," he said.

“I would say of all the drugs I’ve seen — cocaine, amphetamines, heroin, Oxycontin — this is the absolute worst."

"It’s five-dollar insanity," he added.

The damage can be permanent. Paranoia and attention deficits can linger for months. Hall said some drug treatment sessions can only be 20 minutes long because that's all a flakka survivor can stay focused.

Broward County accounts for 20 percent of flakka cases nationwide, he said. The drug has been spreading toward Palm Beach County, Miami-Dade County and Orlando, Hall said.

Outside of Florida, where the substance is sometimes called "gravel," clusters of cases have also been seen in big cities like Chicago, Houston and New York City and in more rural states like Kentucky.

What's so alarming is how quickly it gains ground. In 2013, Broward County's crime lab tested just seven samples of flakka that was seized or found in fatalities. By 2014, that was up to 576, and it's topped 900 so far this year, Hall said.

He remembers how little more than a year ago authorities weren't even sure how it was spelled. The thought it might be flaca, the Spanish word for skinny, but eventually figured out its etymology.

“Flakka spelled with a K is a Hispanic colloquial term referring to a beautiful, slender, elegant woman who charms all that she meets," Hall said.

And, he added, "this charmer is a killer.”