Rainfall totals are expected to range between 80mm and 150mm across much of the region, with some areas likely to receive more than 150mm.
Heavy rain was already recorded across southern Vietnam on May 29, with rainfall reaching 226.2mm in An Giang Province and 202.2mm in Ca Mau Province.
In HCM City, rain began early in the morning and persisted throughout the day. Several monitoring stations recorded significant rainfall, including 97.4mm at Bau Lam and 93.6mm at Phuoc Hoi.
Weather authorities warned that continued rainfall could trigger flooding in low-lying areas and locations along rivers and canals.
Residents were also advised to remain alert to the risk of lightning, strong winds, hail and possible whirlwinds during thunderstorms.