The reigning champion opened with 22.46 metres before unleashing his winning effort of 23.34m in the third round, adding 34 centimetres to the previous best mark set by New Zealand's Jackson Gill in 2013.

His final attempt appeared to have gone even further, but it was ruled a foul after he stepped out of the circle.

"Now I'm really glad because I've broken the world under-20 record and defended my world under-20 title," said Bukowiecki. 

"I have cried after a competition for the first time because of happiness."

Romania’s Andrei Toader was Bukowiecki’s nearest challenger with a national under-20 record of 22.30, while the United States’ Bronson Osborn came third with a personal best 21.27m.

Also winning gold today was China’s Ma Zhenxia, who took the women’s 10,000m race walk crown in a world under-20 leading time of 45 min 18.45sec.

Ma, who topped the 5,000m race walk podium at the Nanjing 2014 Youth Olympic Games, became the first Chinese winner of the title since Liu Hong in 2006.

Runner-up Noemi Stella of Italy finished in a season’s best time of 45:23.85, while Ethiopia's Yehualeye Beletew took bronze with an African under-20 record of 45:33.69.

The third and last final of the day saw Kenya’s Rodgers Kwemoi triumph in the men’s 10,000m with a championship record time of 27:25.23.

Eritrea’s Aron Kifle was forced to settle for silver in a national under-20 record of 27:26.20, while Uganda’s Jacob Kiplimo took the bronze in a personal best 27:26.68.

"I came here expecting to win," said Kwemoi.

"I took the race out fast because I felt that would give me the best chance.

"Once we were on the last lap I knew I would take it."

Action in Bydgoszcz is due to continue tomorrow with finals scheduled in the women’s shot put, 3,000m and javelin throw as well as the men’s long jump and 100m.