It made landfall along the coast of Maoming City in China's Guangdong Province at around 3 p.m. Saturday, Chinese newspapers reported.
At 4 p.m. it lay centered around 320 kilometers to the east of Quang Ninh Province, home to Ha Long Bay, with a maximum wind speed of 117 kph, according to the National Center for Hydro-Meteorological Forecasting.
It will move northwest at a speed of 10-15 kph and is expected to weak into a tropical depression by Sunday morning with winds decreasing to 61 kph.
Vietnam’s northeastern region should expect rains of 40-80 mm, and more than 100 mm in some places, between Saturday evening and Sunday.
A day earlier weather experts had expected the region to be hit by torrential downpours of up to 150-350 mm a day. Rainfall of 180 mm a day is considered heavy.
Chaba is the first storm to appear over the East Sea this year. June-October is normally the rain and storm season in Vietnam.
Some 10-12 storms are expected to enter Vietnamese waters this year, with around half making landfall.