Vietnamese state broadcaster VTV said the torrent of water gushing down from a mountain in Lao Cai province Tuesday buried Lang Nu hamlet with 35 families in mud and debris.
Only about a dozen are known so far to have survived. Rescuers have recovered 16 bodies and are continuing the search for about 40 others.
The death toll from Typhoon Yagi and its aftermath has climbed to 141 as 69 others remain missing and hundreds were injured, VTV said.
Yagi was the strongest typhoon to hit the Southeast Asian country in decades. It made landfall Saturday with winds of up to 149 kph (92 mph) and despite weakening on Sunday, downpours have continued and rivers remain dangerously high.
Floods and landslides have caused most of the deaths, many of which have come in the northwestern Lao Cai province, bordering China, where Lang Nu is located.
"Four people have died and 14 have gone missing" since heavy rains began on Friday in the province of Tata, some 740 kilometres south of Rabat, a local official told AFP, saying the toll could potentially rise.
"Eight houses were washed away by floods in some valleys" near Tamanart, a rural area in the Tata region, said the official, who did not wish to be named.
Usually arid areas in southern Morocco and Algeria have been drenched in floods caused by massive rainfall since Friday, officials told AFP Sunday.
Areas in southern Morocco have been affected "by an extremely unstable tropical air mass", the spokesman for the Moroccan General Directorate of Meteorology, Lhoussaine Youabd, told AFP.
This "led to the formation of unstable and violent clouds" that caused massive rainfall, he said.
Youabd described the phenomenon as "exceptional" and said the areas saw "heavy thunderstorms and significant rainfall, leading to river flooding" as "humid tropical air masses moved northward".
As a result, the Ouarzazate region received 47 millimetres of water in three hours, and Tagounite, near the Algerian border, some 170 millimetres, according to the Moroccan weather service.
The heavy rains hit regions of Morocco that have been suffering from drought for at least six years.
In neighbouring Algeria, authorities meanwhile confirmed one person dead and one missing in flooding in the south.
Algerian civil defence said an unnamed young girl was swept away by the waters in Illizi, in the far south, and another person who was trapped in a vehicle was still missing.
It also said it had rescued several families trapped by flooded rivers, mostly in Illizi and Bechar, also in the south.
Videos posted on social media showed that some areas in the Sahara desert were drenched.
In Morocco’s Ouarzazate, entire streets were flooded.
"We haven’t seen such rain for about 10 years," Omar Gana, a local, told AFP.
Morocco has been experiencing severe water stress after six consecutive years of drought, shrinking dam levels to less than 28 percent of capacity by the end of August.
The rains were accompanied by strong winds, reaching up to 100 kilometres per hour in Ouarzazate and 76 km/h in Marrakesh, where they caused "an optical phenomenon, giving the sky an orange tint", according to the General Directorate of Meteorology.