A 15-year-old boy's death-defying plunge from the top storey of an apartment block was the latest in a string of serious incidents involving students of King's College.

Headmaster Bradley Fenner said the Year 10 student's admission to hospital after falling 50m from his family's 16th-floor Manukau apartment capped a "horrific" year of incidents for the school.

Three students from the private college in the South Auckland suburb of Otahuhu have died since February.

But Mr Fenner said the school was trying to look on the bright side, and staff and students were "delighted" at the boy's escape from death.

"[His] friends will be shaken up. But we are celebrating his miraculous survival, and we're looking forward to having him back amongst us at school."

Yesterday, the teenager's parents and doctors could barely believe it when he began walking in Middlemore Hospital.

He was admitted on Thursday night with several broken bones, a gashed leg and internal injuries after the unexplained fall from Proximity Apartments on Amersham Ave.

He will be released from hospital care on Friday, and is expected to make a full recovery.

The boy dropped 14 storeys from the apartment balcony on the corner of the complex. After a fall of three seconds, he hit the steel roof of the carpark below at an estimated 100km/h.

The roof broke his fall and probably saved his life, said witnesses.

Judging from the nature of his injuries, it is likely that he fell feet-first.

He smashed through the carpark roof, cladding and metal webbing before dropping another two storeys to a concrete floor.

Building manager Jason Epps-Eades said the boy's luck became even more apparent when the site of impact was viewed from above - he fell into the middle of long-run roofing, in a spot which would provide the most cushioning. He also missed all of the concrete girders holding the roof up.

A tenant who saw the boy plunge past his balcony raised the alarm.

The cause of the fall is not known. Counties Manukau police inspected the balcony and were satisfied it was safe. A spokeswoman said police were taking no further action.

The chest-high balcony was made of glass, topped by a steel pipe which was fixed to the apartment's walls.

Medical experts called the teenager's survival a miracle.

St John's medical director Tony Smith said large numbers of New Zealanders died after falling from ladders, trees and roofs every year.

"So for someone to live after this is clearly extraordinary."

Dr Smith said the only comparable example that he had witnessed was a man who fell from the ninth storey of an Auckland apartment complex.

The man struck a canopy on every level, before crashing through a roof onto the ground. He survived almost unscathed.

Neil Thomson, associate professor at the University of Otago's physics department, spelled out the unlikely escape from more serious injury or death.

He said a person falling from 45 to 50 metres would reach a speed of 100km/h by the time they struck the ground.

Coming to rest over 5 metres mean the person's force of impact would have been approximately 10 g - twice as strong as slamming on the brakes in a Formula One car at full speed.

"If someone came to rest over a shorter space, against a harder surface, they would have almost no chance of surviving."

February 2010 - William Thode, 15, died of a rare viral infection of the heart. He was found dead in his bed in his dormitory at the school.

May 2010 - James Webster, 16, died after binge-drinking neat vodka outside a party in Grey Lynn.

May 2010 - Michael Treffers, 15, died in Auckland Hospital after an incident on the Market Rd overbridge on the Southern Motorway.

July 2010 - Student, 15, falls 16 floors from family's Manukau apartment and is hospitalised with minor injuries.