Sinopharm Group Co, China's biggest drug distributor, will sell as much as a fifth of its H-share capital to raise up to HK$4 billion ($515 million) to expand its sales network.

The company will place as many as 165.7 million shares at HK$24.60 each, Sinopharm said in a filing to the Hong Kong Stock Exchange on Thursday.

Shares of the Shanghai-based company fell the most in almost three years after the announcement. The money raised will be used for "the expansion of pharmaceutical distribution and retail network and replenishment of liquidity after the expansion," Sinopharm said in the statement.