SYDNEY (Reuters) - Canada's Saputo Inc (>> Saputo Inc.) extended its offer for Australia's Warrnambool Cheese and Butter Factory Holdings Co (>> Warrnambool Cheese & Butter Factory Co.) on Friday, just hours before the bid deadline, ensuring the heated battle for the country's oldest dairy firm will wage on.

Saputo announced a two-week extension for its A$515 million ($458 million) offer until January 22 and reserved the right to extend it further, keeping up the pressure on bidding rival Murray Goulburn Co-operative Co Ltd.

At stake is a platform for rapidly growing sales of both traditional dairy products and high-tech milk extracts into China.

Saputo, Canada's largest dairy firm, is now the biggest shareholder in Warrnambool with acceptances worth 21.39 percent of the company.

That puts it just ahead of former bidder Bega Cheese Ltd, which holds 18.8 percent of the company, and Murray Goulburn, which owns 17.7 percent. Japanese beverage giant Kirin Holdings Co Ltd (>> Kirin Holdings Company, Limited.) holds a further 10 percent.

Saputo's unconditional cash offer of A$515 million ($461 million), backed by Warrnambool, will rise as high as A$549 million ($492 million) if it receives acceptances of 90 percent or more of Warrnambool shareholders.

Murray Goulburn's A$530 million bid is dependent on regulatory approval, which is not expected until the end of next month. The company has said it may increase its stake in Warrnambool via market purchases.

Bega, which kicked off the bidding war in September but dropped out last month, has yet to decide what it will do with its stake. Bega Chief Executive Barry Irvin said on Thursday it will consider both its shareholders and the broader market.

Irvin has sided with Murray Goulburn in its submission to the Australian Competition Tribunal, saying it did not believe a takeover by Murray Goulburn would lessen competition.

Kirin bought its stake in October to protect its distribution agreement with Warrnambool and has said it will not use it as a "foothold to become involved in a bidding war". ($1 = 1.1253 Australian dollars)

(Reporting by Jane Wardell; Editing by Edwina Gibbs)