Anglo-Dutch consumer goods giant Unilever will pay as much as $5.4 billion to raise its stake in its Indian unit, Hindustan Unilever, to up to 75% in a bet on fast-growing spending power in Asia's third-largest economy.

Unilever said it would acquire up to 487 million shares, or 22.52% of the equity, of Hindustan Unilever in an open offer for 600 rupees a share, 20.6% premium to Monday's closing price.

"This represents a further step in Unilever's strategy to invest in emerging markets and offers a liquidity opportunity at what we believe to be an attractive premium for existing shareholders," Unilever's chief executive, Paul Polman, said in a statement.

Indian law requires a minimum public shareholding of 25% for a publicly listed company.

The offer, payable in cash, is expected to begin in June 2013 and at $5.4 billion would be the largest equity offer ever in India.

HSBC is the manager to the offer.

"It makes a lot of sense to increase stake if the company is serious about staying here for long term," said G. Chokkalingam, chief investment officer of Centrum Wealth Managers, which bought a small stake in Hindustan Unilever after the company reported results on Monday.

"In the long term, we expect there will be more incentive for the parent company to share technology to the Indian unit, introduce more brands here and raise market share," he said.

Last November, GlaxoSmithKline offered to buy an additional 31.8% stake in its India consumer products business for about $940 million.