The world's biggest brewer, Belgian-Brazilian giant AB InBev, is planning a takeover bid for the next largest SABMiller, the companies revealed Wednesday, sending their shares soaring.

"The board of SABMiller notes the recent press speculation and confirms that Anheuser-Busch InBev has informed SABMiller that it intends to make a proposal to acquire SABMiller," said a statement from the British group.

AB InBev confirmed an approach had been made about a possible bid, but said there was "no certainty" of a deal.

SABMiller shares rocketed by more than a fifth in value, while AB InBev jumped around seven percent.

SABMiller, the maker of Foster's, Miller and Grolsch beers, said its board "will review and respond as appropriate to any proposal which might be made".

AB InBev, which brews beers Budweiser, Corona and Stella Artois, was formed in 2008 by the merger of Belgian-Brazilian group InBev and US brewing giant Anheuser-Busch.