The index started off in the red and continued to fall throughout the rest of the day, closing with a 45-point drop, after climbing to a six-week high on Thursday.
The largest loss in a day since July 19 came as Vietnam recorded the highest single-day Covid-19 tally at over 10,600 cases Thursday.
Trading value on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, surged 50 percent to VND38.45 trillion ($1.68 billion), the highest this year.
All 30 tickers in the VN30 basket, which comprises the largest companies, ended in the red, led by GVR of Vietnam Rubber Group, down 6.3 percent.
VIC of biggest private conglomerate Vingroup lost 6.1 percent and pulled VN-Index down 5.7 points.
STB of HCMC-based lender Sacombank lost 5.5 percent to the lowest since July 22.
Strong losses were also seen in MWG of electronics retail chain Mobile World, down 4.9 percent, and ACB of Asia Commercial Bank, down 4.8 percent.
Foreign investors were net sellers for the ninth session in a row to the tune of VND755 billion, with strongest pressure on HPG of steelmaker Hoa Phat Group and VJC of budget airline Vietjet.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, lost 2.31 percent while the UPCoM-Index for the Unlisted Public Companies Market fell 2.12 percent.