CITIC Securities Co. , China's biggest listed brokerage, plans a public share offer that may raise around 19 billion yuan ($2.5 billion) to help boost its capital and expand its business.

The company said on Tuesday that it would issue up to 350 million new A shares, which would account for as much as 11 percent of its expanded share capital.

The shares will be sold at no less than their average market price over the 20 days before the release of the prospectus, and no less than their average price on the previous day. A date for the offer, which needs shareholder approval, was not set.

The shares closed in Shanghai on Monday at 54.07 yuan each, down 16 percent over the past four trading days because of a stock market plunge triggered by a hike in the stock trading tax.

CITIC Securities also said it would pay up to 400 million yuan to buy 35.725 percent of fund management company China Asset Management Co. from Southwest Securities Co.

The purchase will make CITIC Securities the largest shareholder in China Asset Management with 40.725 percent, the official China Securities Journal said. ($1= 7.648 Yuan)