Oil prices succumbed to concerns of a supply overhang, erasing modest early gains as analysts said a persistent global surplus of crude would keep pressuring the market.
Energy stocks fell with PetroVietnam Gas down 2.28 percent and PetroVietnam Drilling & Well Service Corp lower 5.67 percent.
Lender BIDV plunged 6.51 percent on worries over its loans to property group HAGL, whose financial solvency has been a matter of concern to investors.
HAGL shares dropped 6.67 percent to a record low of 8,400 dong ($0.3753).
Analysts expect the index to decline further to 500 points due to a lack of supportive news, while investors keep an eye on the ongoing Party Congress.