Johannesburg - Former world heavyweight champ Lennox Lewis has hailed South African heavyweight boxer Corrie Sanders as a "tremendous fighter".

GALLERY: Sanders in pictures

VIDEO: Sanders knocks out Klitschko

The former WBO champion Sanders died on Sunday morning after being shot when a group of armed men entered the restaurant where he was celebrating the 21st birthday of his nephew with other family members in Brits, North West.

Lewis, the former undisputed heavyweight champion from Britain, said he was stunned "by the tragic death of my friend Corrie Sanders."

"He was (a) tremendous fighter inside the ring and a great man outside of it. The world's boxing fraternity has lost a brother, an ally, and a voice in South Africa," Lewis said.

Current heavyweight titleholders Vitali and Wladimir Klitschko also paid tribute to Sanders on Monday.

Sanders, who was 46, was one of only three men to beat Wladimir Klitschko when he knocked out the younger Klitschko brother in the second round for a shock victory to claim the WBO title in Germany in 2003. He was stopped by Vitali for the vacant WBC belt in 2004 after an eight-round battle in Los Angeles.

"We will remember Corrie as a great person both inside and outside the ring. He was a great fighter with a big heart who always positively represented the sport of boxing," the Ukrainian brothers said in a joint statement.

Police had yet to make any arrests by Tuesday.

Eyewitnesses said Sanders had lain down in front of his teenage daughter to protect her from the bullets when he was shot.