The storm came ashore on Monday morning in northern coastal province Ha Tinh and forecasters said it would move inland before weakening as it pushed northwest toward the hilly regions of Ha Tinh and neighbouring Nghe An.
Bualoi has left at least 20 people dead in the central Philippines since Friday, mostly from drownings and falling trees, and knocked out power in several towns and cities, officials said. It forced about 23,000 families to evacuate to more than 1400 emergency shelters.
In Vietnam, the typhoon was expected to bring winds of up to 130km/h, storm surges of more than a metre and heavy rains that could trigger flash floods and landslides.
State media reported that more than 347,000 families had lost power because of the storm. Strong gusts ripped off corrugated iron roofs along the highway and toppled concrete pillars. In Phong Nha commune, about 45km from Dong Hoi, residents described "terrible gusts" of wind and pounding rain.
Authorities grounded fishing boats in the northern and central regions and ordered evacuations. State media reported coastal city Da Nang planned to relocate more than 210,000 people, while Hue to its north prepared to move more than 32,000 coastal residents to safer ground.
The Civil Aviation Authority said operations were suspended at four coastal airports, including Danang International Airport, with several flights rescheduled.
Heavy rains have drenched central provinces since Saturday night. In Hue, floods swamped low-lying streets, storms ripped off roofs and at least one person was reported missing after being swept away by floodwaters.
In neighbouring Quang Tri province, a fishing boat sank and another was stranded while seeking shelter. Nine people have been rescued while efforts were underway to reach two others at sea, state media said.
A 16-year-old was also killed on Sunday in the province by electrocution during heavy rain and strong winds. He was travelling with a friend on a village road when the accident happened.
The storm is likely to move slowly, bringing longer periods of wind and rain and raising risks of damage and flooding, said Dr. Hoang Phuc Lam, deputy director of the National Center for Hydro-Meteorological Forecasting, according to a government newspaper.
Forecasters warned of more heavy rain through to Wednesday, raising risks of flooding and landslides in northern and central provinces.
Bualoi was the second major storm to threaten Asia in a week. Typhoon Ragasa, one of the strongest to hit in years, left at least 28 deaths in the northern Philippines and Taiwan before making landfall in China and dissipating Thursday over Vietnam.
