It is expected to make landfall imminently, bringing waves of up to 8m (26 ft), according to Vietnam's weather bureau.
Thousands of people who live in coastal communities have been asked to evacuate, and Deputy Prime Minister Tran Hong Ha has urged local officials to treat the storm with urgency.
The AFP news agency says officials are knocking on doors and warning people to flee.More than 50 flights in Vietnam have been cancelled or rescheduled, according to national flag carrier Vietnam Airlines.
About eight airports in the central region, including the international airport in Da Nang, have either suspended operations or are preparing to do so, aviation authorities say.
Before making landfall in Vietnam, Kalmaegi left a trail of devastation in the Philippines - and at least 114 people dead.Before making landfall in Vietnam, Kalmaegi left a trail of devastation in the Philippines - and at least 114 people dead.
Philippines President Ferdinand Marcos Jr has declared a state of emergency - the threshold of which involves mass casualty, major damage to property, and disruption to means of livelihoods and the normal way of life for people in the affected areas.
The typhoon, known locally as Tino, ripped through the populous island of Cebu, submerging entire towns and sweeping cars through the streets. Tens of thousands of people have been evacuated, others are resting in shelters.
Philippines President Ferdinand Marcos Jr has declared a state of emergency - the threshold of which involves mass casualty, major damage to property, and disruption to means of livelihoods and the normal way of life for people in the affected areas.
The typhoon, known locally as Tino, ripped through the populous island of Cebu, submerging entire towns and sweeping cars through the streets. Tens of thousands of people have been evacuated, others are resting in shelters.