SEOUL (Reuters) - Shares of Korea Zinc hit on Friday a fresh all-time high after rising by as much as 29%, extending gains on the bet the company faces a lengthy takeover battle for a controlling stake in the world's biggest zinc smelter.

Korea Zinc's top shareholder Young Poong and private equity fund MBK Partners plan to call for an extraordinary shareholder meeting this year to seek approval to appoint board nominees, a top executive at the fund told Reuters, escalating the takeover battle.

Young Poong and MBK hold a stake of about 38.5% in the company.

Korea Zinc, which reportedly has about a 34% stake supportive of the current management, has not yet disclosed the outcome of its 3.2 trillion won ($2.4 billion) tender offer to buy its own shares, which expired on Wednesday.

On Thursday, when Korea Zinc shares surged 29.9% to the daily upper limit, retail investors purchased shares worth 3.6 billion won. Institutional investors, foreign buyers and "other corporations", which supposedly include the company itself, sold, according to analysts.

"For now, there are so many factors affecting stock prices, from retail buying to buy-backs. We should be able to make initial assessment after Korea Zinc's tender offer result," said Kim Yoon-sang, an analyst at iM Securities.

Trading on Friday was volatile. Korea Zinc shares were up 10.2% as of 0245 GMT, after rising as much as 29% earlier in the session to reach a high of 1,470,000 won.

(Reporting by Jihoon Lee; Editing by Ed Davies)