Tim Mikkelson believes Sonny Bill Williams can make the difference for New Zealand in the rugby sevens tournament at Rio 2016.

Williams switched codes at the start of the year with the Olympic Games in mind and he made an immediate impact with a try on his sevens debut.

Rugby returns to the Olympic schedule for the first time since 1924, presenting Williams, 30, with the chance to add a gold medal to his two Rugby World Cup triumphs.

He impressed during the recent World Rugby Sevens Series in London, and captain Mikkelson believes he could provide the added spark the Kiwis need to take gold if he is selected.

"He's very powerful and he can do stuff that no one in the team is able to do," Mikkelson said at a promotional event in Rio.

"He has also shown that he can make very big tackles. He's grown the game of rugby worldwide and it would be awesome to have him in the squad."

New Zealand coach Gordon Tietjens is expected to name his 12-man squad for the Games in June.