TOKYO (REUTERS) - Japanese teenager Abdul Hakim Sani Brown is eyeing bigger scalps at the World Championships in London after completing an impressive sprint double of national titles over the weekend.

In pouring rain, the 18-year-old upset members of Japan's Olympic silver medal-winning 4x100m relay team to win the 100m in a personal best 10.05sec in Osaka on Saturday.

On Sunday, he ran a personal best 20.32sec to seal the 200m, two years after making the semi-finals at the World Championships in Beijing.

No Japanese sprinter has ever broken the 10-second barrier in the 100m, with Koji Ito coming closest when he ran 10sec flat in 1998.

But former junior 100 and 200m world champion Sani Brown is emerging as the man most likely to do so and will be keen to test the barrier in London in August.

"Even I'm surprised," said Sani Brown of his weekend. "I didn't know I could run like this. I hope I get the chance to compete against top sprinters and break the 10-second barrier."

Born to a Ghanaian father and Japanese mother, Sani Brown became the first to complete the national sprint double since Shingo Suetsugu's 2003 sweep.

Injury robbed the 2015 International Association of Athletics Federations 'Rising Star of the Year' of a run at the Rio Olympics, where the 4x100m relay team shot to national fame after winning silver behind Usain Bolt's Jamaica.

Having graduated from high school in March, Sani Brown is now training in the Netherlands with Rana Reider and will move to the United States after enrolling with the University of Florida.

"I think there's a difference in the way coaches work in Japan and the way the top coaches in the world work," the 1.88m-tall Sani Brown said in comments published by Japanese news agency Kyodo on Monday.

"I've done a lot of weight training which has strengthened my core, and that's stabilised my upper body when I run."

Ito, now a high performance chief at Japan's athletics federation, said the sprinter had the nous of a seasoned campaigner.

"Like Carl Lewis or Bolt, he has the ability to rein it in until 60 or 70m before letting it all go, and that is a quality not everyone has," Ito told Kyodo.

Sani Brown's biggest test may be coping with the hype when he lines up at London.

Goal-setting is unlikely to be a problem.

"I'm very happy about being No. 1 in Japan, but I don't want to settle for this," he told Kyodo.

"I want to do well at the world championships and other competitions I've got ahead of me."