Top seeds Han Chengkai and Zhou Haodong will aim for boys' doubles glory for China ©BWF/Facebook

The number one and two boys' seeds were knocked out at the semi-final stage on the penultimate day of action at the Badminton World Federation (BWF) World Junior Championships at the Bilbao Arena in Spain.

Thailand's number one seed Kantaphon Wangcharoen had not dropped a game up until this point but came unstuck against China's Sun Feixiang today, who triumphed 21-9, 21-13.

The fifth seed will now play Indonesia's 14th seed Chico Aura Dwi Wardoyo in tomorrow's final, after he accounted for Malaysia's second ranked player Lee Zii Jia.

Wardoyo won 21-19, 21-18 in a tight clash to book his place in the final.

In the girls' tournament, the semi-finals went according to form as the best ranked players left progressed from each last four contest.

China's second seed Chen Yufei proved too strong for Kim Ga-eun of South Korea, progressing thanks to a 21-12, 21-17 success.

She will now meet third seed Pornpawee Chochuwong of Thailand for the title, who knocked out Japan's Natsuki Oie after a marathon first game, 27-25, 21-19.

The Chinese, who won the mixed team title in Bilbao, will have the chance to win all five prizes on offer tomorrow after also reaching the showpiece games of the three doubles events.

Sayaka Hobara and Nami Matsuyama made the girls' doubles final for Japan ©BWF/Facebook
Sayaka Hobara and Nami Matsuyama made the girls' doubles final for Japan ©BWF/Facebook

In the boys' doubles, top seeds Han Chengkai and Zhou Haodong moved through by defeating Thailand's third seeds Pakin Kuna-Anuvit and Natthapat Trinkajee 21-15, 21-12.

They will now meet unseeded South Korean duo Lee Hong-sub and Lim Su-min who accounted for another Chinese pairing, Fan Qiuyue and Ren Xiangyu, 21-15, 17-21, 22-20.

The girls' doubles final will be a contest between the top two seeds with China's number-one ranked duo Du Yue and Xu Ya successful today against South Korea's Ga Eun Kim and Hyang Im Kim, 21-15, 21-8.

Second seeds Sayaka Hobara and Nami Matsuyama of Japan saw off Indonesians Yulfira Barkah and Jauza Fadhila Sugiarto 21-14, 21-13.

China are already assured of mixed doubles gold with top seeds He Jiting and women's doubles finalist Du set to meet compatriots Zhou, the boys' doubles finalist, and Hu Yuxiang. 

The former pair came through 21-14, 21-11 against Tang Jie Chen and Ee Wei Toh of Malaysia, with the latter beating South Koreans Kyung Hoon Park and Hye Jeong Kim, 21-17, 21-18.