Intense rainfall since early October has caused floods and mudslides that have killed more than 70 people in central Vietnam.
A landslide left at least 22 military personnel missing in Vietnam's central province of Quang Tri.
The government said early on Sunday that it could be the largest military loss in peace time as the country battles the worst flooding in years.
Heavy rain has pounded the region for more than a week, and over 70 people have been killed in floods and landslides, according to Vietnam's disaster management authority, with concerns mounting that waters could rise further.
The missing soldiers are believed to have been buried underneath thick mud, according to the government's official website.
"From 2am, there have been four to five landslides, exploding like bombs and it feels like the whole mountain is about to collapse," said local official Ha Ngoc Duong, according to the VnExpress news site.
General Phan Van Giang, the army's chief of general staff, warned there could be further landslides in the area and said rescuers needed to find a safer way to access the site.
Five bodies have been recovered so far, state media added.
Deadly Vietnam landslides
It comes just days after 13 members of a rescue team were found dead after a failed attempt to save workers from a hydropower plant engulfed by a landslide.
The bodies of two employees at the plant have been found but 15 are still missing.
River levels in Quang Tri had reached their highest in two decades, state media said. The disaster management authority raised its risk alert warning to the second highest level on Sunday, warning of further flooding and landslides.
Vietnam is prone to natural disasters and regularly suffers more than a dozen storms each year, often bringing flooding and landslides.
More than 130 people were reported dead or missing in natural disasters around the country last year, the General Statistics Office said.
'Another another sleepless night'
"We had another sleepless night," an emotional deputy defence minister, Phan Van Giang, told reporters on Sunday.
The government later said the bodies of three of the missing personnel have been recovered.
"We've never lost so many military members, including two generals and high ranking officials, in natural disasters," the government of the Southeast Asian nation said in a F acebook post.
State media on Sunday reported rivers in Quang Tri province rose to the highest water levels in over 20 years.
In Thua Thien Hue province, rescuers battled driving rain in search of at least 15 construction workers missing after a landslide at the start of the week in a mountainous area.
Rain of as much as 600 millimetres is likely to continue in parts of central Vietnam until Wednesday, the country's weather agency said on Sunday.