Big money managers led by Fidelity Investments are close to launching a private trading venue designed to let them buy and sell large blocks of stock without the involvement of Wall Street firms and high-speed traders, according to people familiar with the matter.

Nine firms including BlackRock Inc. BLK, +1.55% , Bank of New York Mellon Corp. BK, -0.45% , J.P. Morgan Chase & Co. JPM, -0.21% and T. Rowe Price Group Inc. TROW, +0.40% , are forming a company that will operate a “dark pool” — a private trading venue in which activity takes place outside of the public view — the people said.