Typhoon Kalmaegi made landfall in Vietnam on Thursday after killing at least 114 people and flooding entire towns in the Philippines.
More than 260,000 soldiers are on standby for rescue efforts as winds of up to 92 mph (149 km/h) hit the country's coastline, according to Vietnamese media and the government's online portal.
Six airports in the country have been forced to close, and hundreds of flights are expected to be affected, the government warned.
The country, which has already been battling record rains and floods, is now facing one of Asia's strongest typhoons this year.
The typhoon could generate waves of up to 8 m (26 ft) on the South China Sea, according to Vietnam's weather bureau.
The country's environment ministry stated that the storm is on land, in the provinces of Dak Lak and Gia Lai as reported by various outlets, including the AFP news agency.
Hundreds of localities in seven cities and provinces are at risk of flooding and landslides in the next six hours.
There have already been reports of damage from several provinces, including roofs torn off homes, shattered glass panels at hotels, and trees uprooted along city streets and rural roads by powerful gusts.
In the Quy Non area, trees have fallen on main roads, and windows in hotels have smashed.
The typhoon made landfall in Vietnam at 19:29 local time (12:29 GMT). About 30 minutes later, hundreds of residents in two communes of Dak Lak province called for help, local media reported.
Many people reported that their homes had collapsed or been flooded while strong winds and heavy rain continued to batter the area.
Dak Lak province is approximately 350 km (215 miles) northeast of Ho Chi Minh City.
Vietnam's military has deployed over 260,000 soldiers and personnel, along with more than 6,700 vehicles and pieces of equipment, including six aircraft, to help with storm relief efforts.
On Wednesday morning, a reporter from AFP observed officials warning residents in coastal communities to evacuate.
According to local media, Prime Minister of Vietnam Pham Minh Chinh held an online meeting to direct the emergency response. We must reach isolated areas and ensure people have food, drinking water, and essential supplies, he was quoted as saying. No one should be left hungry or cold.
Before reaching Vietnam, the typhoon, known locally as Tino, left a trail of devastation in the Philippines. At least 114 people were killed and tens of thousands were evacuated, particularly from central areas including the populous island and tourist hotspot of Cebu, where cars were swept through the streets.
Early on Thursday, Philippines President Ferdinand Marcos Jr. declared a state of emergency due to the mass casualties, major property damage, and disruption to livelihoods and daily life for affected citizens.
Vietnam has been grappling with floods and record rains for the past week. Burst riverbanks have flooded popular tourist spots, including the UNESCO-listed city of Hue and historical hotspot Hoi An, where residents have been navigating the city in wooden boats after the Hoai river overflowed.
Seaside communities in Vietnam are expected to be hit hard by Typhoon Kalmaegi. A forecast issued at 16:00 local time (9:00 GMT) by a senior official at Vietnam's National Center for Hydro-Meteorological Forecasting predicts a sea-level rise of 4 to 6 m (13 to 20 ft) in at least two provinces, which could capsize boats and devastate fishing farms.
Meanwhile, deputy director Nguyen Xuan Hien has warned that Typhoon Damrey, which struck Vietnam in 2017 with less intensity than Kalmaegi but still caused severe damage, should serve as a warning, urging people to remain highly alert. Thailand is also preparing for the storm's impact, having warned of flash floods, landslides, and river overflows.
