A unit of Swiss speciality chemicals firm, Clariant International, has made an open offer to buy a 20 per cent stake in India's Colour Chem Ltd at Rs 318 share, the Bombay Stock Exchange said on Monday.

The offer will be open between May 28 and June 26, according to a release on the exchange's Web site, www.bseindia.com.

It said that EBITO Chemiebetelligungen AG now held a 50.1 per cent stake in the Indian company.

Colour Chem's shares jumped as much as 16.1 per cent on the news to Rs 233.95, still about 36 per cent below the offer price.

The Securities and Exchange Board of India had asked Clariant in October to make the open offer in accordance with the country's takeover rules after the Swiss firm gained a controlling stake in Colour Chem.

Clariant International, a wholly owned subsidiary of Clariant AG, had acquired the chemicals business of Hoechst AG in 1997, and as a result, got the 50.1 per cent stake that Hoechst held in Colour Chem.

It had sought to be exempted from Indian takeover rules, which require an acquirer of a controlling stake in a company to make an offer to buy a further 20 per cent stake from shareholders.