The benchmark VN-Index on the Ho Chi Minh Stock Exchange lost 2.91 per cent to end at 725.94 points.
The VN-Index gained 0.25 per cent on Wednesday.
The HNX-Index on the Ha Noi Stock Exchange was down 0.84 per cent to close at 100.99 points.
The northern market index had increased by a total of 2.21 per cent on Tuesday and Wednesday.
More than 447.3 million shares were traded on the two exchanges, worth VND4.80 trillion (nearly US$202 million).
That included nearly 400 million shares traded via the order-matching system, worth VND3.74 trillion.
The local stock market was subdued by strong foreign selling on worries about a global economic recession caused by the COVID-19 pandemic, according to MB Securities Co (MBS).
Circuit breakers were hit on many markets despite central banks’ efforts to provide stimulus packages to stabilise market sentiment, MBS said.
Foreign investors on Thursday net-sold a total of VND525 billion worth of Vietnamese shares, putting heavy pressure on market trading.
Large-cap stocks were hit strongly as the large-cap tracker VN30-Index tumbled more than 3 per cent.
Twenty-seven of the 30 largest stocks by market capitalisation and trading liquidity in the VN30 basket declined while only one increased.
The sell-off also spread to mid-cap and small-cap stocks, pulling the two trackers down 1.86-2.12 per cent.
On the HNX, the HNX30-Index lost 0.95 per cent while the mid/small-cap tracker fell 0.66 per cent.
Retail, banking, mining and energy, insurance, food and beverage, rubber, and utilities were the worst-hit sectors, data on vietstock.vn showed.
In the banking sector, Vietcombank (VCB), Eximbank (EIB), Vietinbank (CTG), Techcombank (TCB) and VPBank (VPB) were the five stocks that suffered the worst falls.
Mobile World Investment Corp (MWG) and PAN Corp pulled the retail industry down.
Other hard-hit large-caps included brewer Sabeco (SAB), dairy producer Vinamilk (VNM), insurer Bao Viet (BVH), petrol firm Petrolimex (PLX) and PetroVietnam Gas (GAS).
MBS said the Vietnamese stock market is still heading down as pressure from international stocks and foreign selling may make investors more cautious.
Thanh Cong Securities Co (TCSC) remained doubtful about the market rebound as the latest developments of the pandemic will still be a burden for investors.