The VN-Index fell 0.5 per cent to 942.34 points, with 191 stocks declining while only 69 increased and 122 remained unchanged.
Among the 30 largest shares by market value and liquidity (VN30), 25 slumped and only four advanced.
Banking, real estate and oil and gas stocks were the biggest losers.
Except Vietcombank (VCB), which closed flat, the seven other lenders in the VN30 lost value. Techcombank (TCB), Sacombank (STB) and Ho Chi Minh Development Bank (HDB) fell hardest, with each down by between 1 and 3 per cent.
Big realty companies like Vingroup (VIC), Vinhomes (VHM), Novaland Investment (NVL), Coteccons Construction (CTD) and Ho Chi Minh City Infrastructure Investment (CII) also decreased between 0.5 and 2.2 per cent.
Among the oil and gas group, the biggest listed gas company PV Gas (GAS) and the PetroVietnam Drilling and Wells Services (PVD) each slipped by less than 1 per cent.
Crude oil prices continued declining on Monday after China reported worse-than-expected economic data which reignited concerns about declining world demand. Brent crude fell US$1.07, or 1.73 per cent, to $60.94 a barrel. West Texas Intermediate (WTI) oil price also fell 1.1 per cent to $51.93 per barrel.
On the Ha Noi Stock Exchange, the HNX-Index inched down 0.12 per cent to 103.38 points.
A total of 91 million shares worth VND1.8 trillion ($77.3) million were traded on the two exchanges in the morning.
The afternoon trading session starts at 1pm.