DOMESTIC stock exchanges have halted processing more than 20 initial public offering (IPO) plans sponsored by Shenzhen-based China Merchants Securities, following an investigation into the brokerage, according to exchange disclosures. The Shenzhen Stock Exchange has suspended 15 IPO plans set for its ChiNext board, while the Shanghai exchange has paused five IPOs targeting its tech-focused STAR Market since last Friday, exchange filings showed. Three other IPOs targeting the Beijing Stock Exchange were also affected. The bourses attributed the halts to an investigation by the China Securities Regulatory Commission (CSRC) into China Merchants Securities, their common sponsor. The CSRC decided to…