China Petroleum & Chemical Corp (Sinopec), Asia's largest refiner, said it plans to raise about $3.1 billion in a share offering to fund its business development, sending its shares sharply lower as investors fretted about the volume of new stock in the market.

Sinopec agreed to sell 2.85 billion new Hong Kong-traded shares at HK$8.45 each, a 9.5% discount to Monday's close and 7.4% below the average closing price over the past 30 days, the company said in a filing to the Hong Kong stock exchange late on Monday..

The shares were sold to a group of about 10 investors that included some of the world's largest institutional investors and global fund managers, a source familiar with the transaction told Reuters.

Sinopec said in its filing that the deal would help the company "enrich its shareholder base by attracting a number of high caliber investors to participate in the placing." It gave no further description of the buyers.

Proceeds from the offering would be used "as general working capital to fund the business development of the company," Sinopec said.

The refiner has been looking to buy overseas assets from its parent Sinopec Group to boost oil and gas production. Fu Chengyu, chairman of Sinopec Group, said last year Sinopec could raise funds from the market to help fund those acquisitions.

Goldman Sachs acted as sole global coordinator and bookrunner for the deal.