New Zealand shot put sensation Jacko Gill has stunned the world by becoming the youngest athlete to send the senior weight shot out over 20 metres.

The 16-year-old was competing at a throwers meeting at the Sovereign Stadium on the North Shore on Saturday, and his second-round effort of 20.01m not only broke Les Mills' 44-year-old New Zealand record but was a world best with the 7.26kg shot for his age group.

Gill beats Michael Carter of the United States by two years seven months as the youngest in the world to break 20m. He is also the first athlete under 100kg (he weighs 96kg) to better 20m with the Olympic shot.

Gill, who competes for the Takapuna Club and lives with his parents in Devonport, is also delighted that he is the youngest to qualify for the world championships and the Olympic Games.

"It was a kind of dream that I would go that far. I've proved the sports scientists wrong who said that it was impossible for a person under 100kg to go over 20m," said Gill.

"I've trained very hard for this, six to seven hours a day. Les Mills is right up there and to get his records is a dream in itself," he added.

Mills' New Zealand resident record of 19.51m was set in Auckland in 1966 and his national record, which Gill broke, was 19.80m set in Honolulu in July 1967.

Britain's Geoff Capes holds the New Zealand allcomers record at 20.76m. He made that throw at Mt Smart Stadium in January 1980, adding two centimetres to his own record set at the 1974 Christchurch Commonwealth Games.

Mills said he was not surprised that Gill had broken his resident and national records.

"I thought Jacko was probably six months off breaking it. I'm delighted he has done it, it was time that record was broken, and by a 16-year-old, that's phenomenal.

"I look at him with a lot of awe, it's not only a physical thing but a huge mental thing that drives a young man like that to train five to six hours a day," said Mills.

"He could be our greatest ever athlete and that's saying something with Peter Snell out there."

Mills believes Gill could be among the medals at next year's London Olympic Games, even aged just 17.

"Who'd know what this young man can do. Never has there been in the history of athletics a thrower like Jacko. He could be the greatest young shot putter ever."

Gill bettered American Arnold Campbell's best by a 16-year-old of 18.72m, set in 1983, and Udo Beyer of Germany's 1973 best of 19.63m by a 17-year-old. Beyer went on to win the gold medal in the shot put at the 1976 Montreal Games and the bronze medal in Moscow in 1980.

Gill's father, Walter, New Zealand's shot put champion in 1987 with 16.05m and in 1989 with 16.19m, said Jacko's performance was incredible.

"He'd done 19.10m in training and was consistently out to 18.60m to 18.70m, so when he did 19.98m in the opening round I thought that was it - he'll have to live with that for the next year, but he's very competitive and has that X-factor.

"To then come out in the next round and do 20.01m, that now ranks him 14th in the world this year, was incredible," said Walter Gill.

Reese Hoffa of the US leads the world rankings with 21.56m. The world record is 23.12m, set by American Randy Barnes in 1990.

Gill's coach, Didier Poppe, described his effort as one of the most incredible performances in the history of world shot putting.

"He was warming up for his competitions next week in New Caledonia," said Poppe.

"It's also a world senior champs qualifier for the world champs in Daegu, Korea but the IAAF rules don't allow Jacko to compete there because he's too young.

"If he was a runner or a jumper he'd be allowed to participate, but as a thrower he isn't," added Poppe.

"We were certainly expecting throws over 19m as seen several times in training, but 20m is such a symbolic line that very few throwers in the world are able to beat, and when one remembers that Jacko broke the 20m line with a 5kg shot only 16 months ago in Timaru, and the 20m line with the 6kg shot only nine months ago in Moncton [Canada], this is the most incredible progression ever seen."

Gill, the world junior champion, will aim to add the youth title when he competes at the world youth championships in Lille, France, early in July.

* The rules for the world championships in Daegu in August state that any athlete aged 16 or 17 years on December 31, 2011, may compete in any event except the men's throws, decathlon, 10,000m, marathon and race walks.

* World best for his age and national record: 20.01m by Jacko Gill on Saturday.

* World record: 23.12m set by Randy Barnes (US) in 1990.

* National record: 19.80m set by Les Mills in 1967.