Former New Zealand centre Sonny Bill Williams has outlined his desire to return to boxing after confirming his retirement from both rugby codes.

The 35-year-old won the Rugby World Cup with the All Blacks in 2011 and 2015, having previously reached the Rugby League World Cup final in 2013.

He regularly switched between codes across his 17-year playing career, which culminated in a second spell with NRL side Sydney Roosters.

As well as enjoying a glittering rugby career, Williams also won all seven of his professional heavyweight boxing fights between 2009 and 2015.

And the cross-code star, recently described as "the best athlete I have coached" by ex-New Zealand boss Steve Hansen, is ready to revive his boxing career.

"I'm keen to get back into the ring. I've got a couple of years," he told the Nine Network. "I spoke to the wife first and... like usual, she supported me.

"I want to know how I will go in six months instead of six weeks."

Williams, who won two NRL Premierships with the Roosters (2013) and Canterbury Bulldogs (2004), played his final game of competitive rugby for the Roosters in October's play-offs semi-final loss to the Canberra Raiders.

Replying to well-wishers on social media on Thursday, Williams said: "A massive thankyou to the public & fans for all the support over years. 

"To my many teammates, thanks for the lessons & help along the way. It wasn't a perfect journey, but the lessons have helped shape me into the man I'm proud to be off the field today."