The index fell by 17 points as of 11:06 a.m. after ending in the red in four out of the last six sessions.
The main bourse Ho Chi Minh Stock Exchange (HoSE) saw 361 tickers in the red and 107 in the green.
Brokerages have forecast earlier that the market would drop in the short term.
The VN30 basket, comprising the 30 largest capped stocks, saw 15 tickers in the red, with SSI of leading brokerage SSI Securities Corporation falling 4.5 percent to the lowest since August last year.
VHM of real estate giant Vinhomes dropped 3.4 percent, lowest in over a year.
Other losers included CTG of state-owned lender VietinBank, down 3.5 percent, MBB of lender MB, down 2.7 percent, and VIC of biggest private conglomerate Vingroup, down 2.9 percent.
Fourteen blue chips bucked the trend, with PNJ of Phu Nhuan Jewelry rising 3.2 percent and FPT of IT giant FPT Corporation gaining 2.2 percent. Both were at new peaks.
They were followed by SAB of brewer Sabeco, up 2 percent, and TPB of private TPBank, up 1.6 percent.
Foreign investors are buying the dips with a VND88 billion net purchase, focusing on DPM of Petrovietnam Fertilizer & Chemicals Corporation and NLG of real estate developer Nam Long Investment Corp.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, was losing 2.51 percent, while the UPCoM-Index for the Unlisted Public Companies Market was losing 1.5 percent.