Six people have been killed in severe flooding sweeping central Vietnam, local officials said Saturday, amid concerns that the inundations could continue to worsen.

Authorities have evacuated some 20,000 people as heavy rains pummelled the country from Quang Tri to Ninh Thuan coastal provinces since Tuesday, according to a regional natural disaster committee.

"The waters rose too fast and so many local residents did not have enough time to prepare," committee director Van Phu Chinh told AFP, adding that the "situation could worsen" over the weekend.

He said three people remain missing in the region.

Several parts of the former imperial city of Hue, a World Heritage site, were under up to 70 centimetres (27 inches) of water.

Last week, Vietnam evacuated nearly 800,000 people before it was hit by a weakened Typhoon Haiyan -- one of the most powerful ever recorded -- which has caused several thousands deaths and huge damage in the Philippines.