A Syracuse grad and a Rhode Island co-ed died after popping ecstasy pills at the wild Electric Zoo music fest — prompting officials to shut down the megaparty, which drew 100,000 ravers to Randall’s Island over the weekend.

“I just took six hits of Molly,’’ tragic 20-year-old Olivia Rotondo told an EMS worker on Saturday, referring to the drug’s street name — before suddenly collapsing in a seizure and dying.

Organizers abruptly canceled yesterday’s revelry just hours before it was scheduled to begin, under pressure from the city.

The deaths of Rotondo, a University of New Hampshire junior from North Providence, RI, and Jeffrey Russ, a 23-year-old Syracuse University graduate from Rochester, took place during a weekend of mayhem that included:

* A 16-year-old girl found under a van with her pants down and taken to a hospital, where tests showed she was sexually assaulted, according to a city parks advocate.

* At least four people hospitalized in critical condition after apparent drug overdoses.

* Thirty-one arrests, mostly for drug possession but also for disorderly conduct and resisting arrest.

NYPD detectives launched a homicide probe into the deaths of Rotondo and Russ, police sources said. The duo were not believed to have attended the event together.

Just hours before her death, Rotondo tweeted her excitement about

attending the fifth annual Electric Zoo. “The amount of traveling I’ve done today is unreal. Just get me to the damn zoo,” she tweeted Saturday.

Her grieving grandfather Henry Rotondo, 73, told The Post, “She was a great kid — that’s all I can tell you.”

Lauren Pezzelli, who lives across the street from the family, called her “a lovely, beautiful young girl inside and out.”

“They’re devastated,” added Pezzelli of Rotondo’s parents, whom she visited earlier in the day. “It’s not meant to be this way.”

Russ’ aunt Patti Fanto-Holdaway said she and other relatives rushed to New York City when they got the grim news.

“We drove down in the middle of the night after we got the call that he was in the hospital,” she her voice trembling. “We lost him before we got there.”

Russ had been staying with a friend in New Jersey since Thursday.

“He loved going to those things and meeting up with his friends,” Fanto-Holdaway told The Post. “One of his [frat] brothers on his Facebook page said, ‘He lit up every room he walked into.’ He was that kid,” she said.

She said the family was told that Russ had taken ecstasy.

Law-enforcement sources said he also had crystal meth in his pocket when he died.

“He had an extremely high fever when he hit the hospital,” Fanto-Holdaway said.

Russ was pronounced dead at Harlem Hospital at 3 a.m. yesterday, and Rotondo passed away at 10:45 p.m. Saturday at Metropolitan Hospital, officials said.

Both thought they were taking ecstasy, the street name for the euphoria-inducing club drug MDMA, but toxicology reports are still pending.

Sometimes, bogus pills peddled as Molly contain no MDMA at all but instead more harmful drugs such as amphetamines or powerful tranquilizers.

“Especially at concerts, when people are buying from strangers, you have no way of knowing what the hell you’re putting down your throat or up your nose,” the source said.

One source said it was unlikely that the duo got the drug from the same dealer given its widespread popularity, adding they may have brought it with them.

Erin Mulvey, a spokeswoman for the US Drug Enforcement Administration, said much of it is shipped here in bulk powder from overseas and then fashioned into pills.

“The DEA is targeting large-scale distributors for bringing quantities of the drug over from China, India and Canada,” she said.

Many Zoo fans, who paid up to $180 a day to attend, were furious to learn yesterday’s performances — slated to include Zedd, Laidback Luke, Armin Van Buuren, Steve Aoki and Sebastian Ingrosso — wouldn’t go on.

“If you cared about your patrons then you wouldn’t disappoint the tens of thousand RESPONSIBLE concertgoers who LIVE for the music at these festivals,” fumed David Eli on the event’s Facebook page.

Some fans blamed the victims.

“If people take drugs, that’s their own fault,” said Dayna Marce, 19, of upstate Highland Falls. “You’re going to sit here and take drugs and die because of it — how’s that my fault that you died? I know that sounds mean, but it’s not fair to me.

“I’ve been looking forward to this for so long. I’m so angry,

“I was looking forward to this all summer. I wanted to see Zedd. I never saw him live before,” Marce griped.

Last night, hundreds of angry ticket-holders tried to restart the party when they showed up for a surprise deejay performance at The Tribeca Grand in Manhattan. Police were called to disperse the crowd, who were raving mad over the cancellation.

“I’m very disappointed. I spent $400 for tickets,” said Maralynn Lopez, who traveled from Chicago.