World Rugby will review the allegation of racism levelled at South Africa hooker Bongi Mbonambi by England flanker Tom Curry during their World Cup semifinal in Paris.

Curry alleges that Mbonambi used a racial slur against him in the first half of the Springboks' 16-15 victory, which set up a final meeting against old foes New Zealand at the same venue on Saturday.

"World Rugby takes all allegations of discriminatory behaviour extremely seriously," the governing body said in a statement.

"We can confirm that we are formally reviewing the allegation made by England's Tom Curry in relation to the use of discriminatory language during the England versus South Africa Rugby World Cup 2023 semifinal on Saturday.

"World Rugby will not be making further comment until the conclusion of the process."

South African Rugby said on Sunday they had launched their own internal investigation, and that they were "reviewing the available evidence".

Audio and video footage posted on social media show Curry complaining to referee Ben O'Keeffe, although no action was taken and the alleged slur is not heard.

Curry confirmed an incident when questioned by reporters afterwards but refused to say what had allegedly been said.

England coach Steve Borthwick also refused to comment on the allegation.

If found guilty Mbonambi is likely to face a suspension, which would be a huge blow to the Boks ahead of the final.

He is their only specialist hooker in the squad after they replaced the injured Malcolm Marx with fly half Handre Pollard, who kicked the winning penalty against England.

Regular loose-forwards Deon Fourie and Marco van Staden are the other hooker options in the squad, but it would be a tall order to ask them to scrum for 80 minutes against a pack as accomplished as New Zealand's.

Reuters