LONDON?Jay Sean is celebrating after becoming the first Indian-origin rapper to top the US charts with his debut single there, after years of "grinding" away in relative musical obscurity.

The 28-year-old Londoner has scored a number one in the Billboard charts with his single "Down", featuring US rapper Lil Wayne, from his forthcoming album "All or Nothing".

His success was all the more impressive since the song knocked the Black Eyed Peas off the top spot of the Billboard Hot 100, which they had held for a record 26 straight weeks, according to the US chart's website.

"This is insane. It's just incredible to have reached number one with my first release in America. It's difficult for me to put into words," Sean wrote on his website, before embarking on a US tour on the back of his chart success.

"My head is spinning. I've been grinding hard for the last seven years releasing records independently and now to have the biggest record in the USA this week, it's just a dream come true," he said.

Sean was born Kamaljit Singh Jhooti on March 26, 1981 in Hounslow, west London, a suburb with a sizeable South Asian population, right under the Heathrow Airport flight path.

He started rapping at the age of 12 but moved into R and B, reportedly due to the difficulties getting into the British rap scene with his Punjabi Indian heritage, and thanks to his talent for singing.

His track "One Minute" caught the eye of Virgin Records, who signed him up. He released his debut album "Me Against Myself" in November 2004 in Britain. It hit number 29 in the album charts, spawned two top 10 hit singles there, while also selling strongly in India.

However, Sean parted ways with Virgin after disagreements over his direction and set up his own record label, Jayded Records.

In May 2008 released his second album "My Own Way", which peaked at number six in Britain.

"I have a heavy fan base in many countries including India. I'm in a minority culture but in many countries, there's still Indians there and they all knew me," he said.

"I realised I had a global fan base so why not make the music myself?"

Part of his following was thanks to Internet, where his first album, "Me Against Myself" -- released in 2004 after he dropped out of medical school and dove full-time into music -- grabbed wide attention.

He then toured Europe and southeast Asia, boosting his fan base -- though never forgetting his roots.

In January, he returned to Hounslow for a surprise concert at his old school, according to the Hounslow Chronicle local newspaper.

He caught the eye of the US hip-hop label Cash Money Records which signed him up to make an album for the American market -- where the single, "Down", has taken the country by storm even before the "All or Nothing" album's release, expected later this year.

"I'm a very positive, optimistic person," said Sean, about the song that had its origins in a conversation that began about the world's wrongs, before moving on to love.

"And (I) thought: let me write a song about the idea that if you've got someone special in your life then nothing else really matters -- how you need to appreciate the little things."

The singer said it was no surprise to his parents when he switched from studying to singing.

"They knew there might be a strong possibility I'd do music," he said.

"They told me, 'The same way you apply yourself to your studies you have to work hard doing music.' That's always stayed with me."

From his double-decker US tour bus, Sean told an MTV interviewer this week about his first reaction to his success.

"When I heard the news I was in London, about to do an interview for radio," he said. "It's been the only time in my career where when I found out, I literally couldn't breathe properly.

"I was so excited. I was so happy."

His hit US single is set for release in Britain on October 26.