Indian corporate giant Tata Steel and Brazil's CSN on Tuesday entered the auction ring for the prized trophy -- Anglo Dutch steelmaker Corus group -- amid reports the bid could go as high as $11 billion.

The nine-round auction called by the UK Takeover Panel to decide the winner between the two suitors began at 2200 hrs Indian time (1630 hrs GMT) and will end the slugfest that has been on for three months.

Tata Steel had bid $9.2 billion (4.6 billion pounds) against CSN's much higher $9.6 billion (4.9 billion pounds) last month, prompting the UK Takeover Panel to intervene and pick the winner through open bidding.

Earlier in the day, Tata Steel's board met presumably to discuss strategy for the auction, besides approving the earnings for the October-December quarter, during which it had submitted its preliminary bid for Corus.

While Tata Sons Director Arun Gandhi along with investment bankers and advisers is camping here, CSN said its team will be based at offices of Lazard, its main investment banker in the West-End office.

If no winner emerges in the first eight rounds of open bidding scheduled to be completed on Wednesday, presumably even by electronic offers, the Takeover Panel will go in for a ninth and final round on February 1.

Under the auction norms, each suitor is required to raise bids by a minimum of five pence per share.

Tata Steel, whose 500 pence a share bid was countered by CSN with 515 pence, would be the first to submit its offer, sources said. Officials of neither Tata nor CSN were available for comments on the extent of their bidding, which could go to a minimum of 600 pence a share if the winner is to be decided by the ninth round.

No matter who wins, the new entity would become the world's fifth largest steel maker on the strength of over 19 million ton steel produced by the Anglo-Dutch steelmaker.

According to Takeover Panel's guidelines, both the bidders -- Tata Steel and CSN -- cannot revise their bid nor make a new bid after the conclusion of the auction process unless a third suitor emerges with a firm intention to acquire Corus.

However, there has not been any third bidder so far with all the potential suitors saying the valuation has already stretched far beyond the fair value for the Anglo-Dutch steelmaker.

But investment banking and legal experts said it would not be a surprise if the loser in the auction prompts a third bidder to launch a bid, so that it can make another attempt at acquiring Corus.

Acquisition of Corus is important for both Tata Steel and CSN, which among other synergies could make the winner the world's fifth-largest steel maker.

Currently, Arcelor-Mittal is the world's largest company in this space, followed by Japan's Nippon Steel, South Korea's Posco and Germany's ThyssenKrupp in the top league.