A water slide at Nicco Park caved in on Tuesday afternoon from a height of 18 feet with about 20 youngsters on it, some of whom had allegedly overpowered the gatekeepers to take the ride together when only one is allowed at a time.

At least four of the revellers, aged between nine and 20, suffered fractures and around 13 were bruised when a portion of the Body Slide, the 76-metre-long serpentine ride in the Wet ‘O’ Wild section of the amusement park, gave way because of overload.

The grass below apparently saved all of them from more serious harm.

Witnesses to the accident that might have been a tragedy said some of those on the fibreglass slide had tried to stand up and do a jig milliseconds before the crash, which occurred at 2.35pm.

“A few attempted to climb the fibreglass track from the bottom end, as if to meet those sliding down halfway through the ride,” said a young man who was awaiting his turn to climb to the starting point, 36 feet above the ground.

Sikander Ahmed, a Class IX student who has a leg fracture, said it was a “free-for-all” with the guards appearing powerless against the surge of people in a rush to take the ride.

“I had slid down the water track only a few metres when I found some people ahead of me stop suddenly. I rammed into them and those behind me rammed into me,” he recounted to Metro.

Kamal Hasan, a 13-year-old boy who suffered a spine injury, blamed those who tried to stand up on the slide for the cave-in. “It happened in a flash. The slide split into two and we all fell on the ground,” he said from his hospital bed.

Sixteen of the injured went to Apollo Gleneagles Hospitals on the Bypass, where three of them were “under observation” till late in the evening. “Faraz Ahmed, 20, Md Shabbir, 19, and Sikander Ahmed, 17, have fractures,” said an official at the hospital.

Md. Imran, who suffered a right-arm fracture, was admitted to AMRI Hospitals in Salt Lake.

Nicco Park officials said about 40 guards were on duty in the water park on Tuesday, about 20 more than on a normal weekday. Six of them were manning the Body Slide, they said.

“About 1,500 people had bought tickets for Wet ‘O’ Wild rides till the accident. It wasn’t just the rush, a section of the crowd was unruly,” an official said.

The guards are supposed to regulate the entry of people into the starting point of the slide but Tuesday afternoon saw crowd management quickly go out of control.

“We maintain a distance of about 70 metres between two persons taking a ride on the Body Slide. The second person is allowed to start sliding from the highest point only when the previous person has almost reached the tail. But some revellers were not adhering to the rules. They entered the arena in a group of 20,” said Pradeep Bose, associate vice-president (engineering), Nicco Parks.

So why didn’t the authorities stop the rides for some time so that order could be restored?

“The unruly crowd came all of a sudden. The rides started at 11am and things were moving smoothly. Suddenly, about 20 people together pushed our guards aside and took the ride. The guards were helpless,” insisted Rajesh Raisinghani, associate vice-president, Nicco Parks.

Injured teen Kamal Hasan said the guards were as much to blame for the chaos as the unruly revellers. “They didn’t stop anyone. How else could I enter?”

Tuesday’s accident wasn’t the first at Nicco Park. A woman in her 50s, Shibani Roy, and a seven-year-old girl Swastika Dey, had fallen off a trolley in the Moon Raker section on January 2, 2010, after it possibly jumped rails during the ride.

Shibani dislocated her right wrist when she crashed into a concrete platform along with the girl. The child escaped unhurt.

The authorities said Shibani fell during one of the sharp turns because she wasn’t holding the handle in front of her. The injured woman said the trolley veered off the track.

Some of those injured in Tuesday’s accident accused Nicco Park of doing little to help them. They hired taxis on their own to reach hospital, the boys said.

Raisinghani contested the allegation, saying the authorities arranged for them to be sent to hospital.

Nicco Park’s official website describes the water slide as “eastern India’s first”, with two straight dips and a curved one from different sections of the same tower.

The descent from 76 metres is covered in seven seconds, according to the description in the website.