Seven people – three males and four females aged four months to 47 years – were swept away by a flash flood triggered by storm Wipha' s aftermath on Xia Stream last Saturday, said authorities in the district of Houaphanh Province.

Viengxay has conducted searches along the stream until the Laos-Vietnam border, but have been unable to find the victims.

As the stream crosses the border into Vietnam's Quan Son District in the central province of Thanh Hoa, Viengxay authorities on Monday sent a letter requesting Quan Son District's assistance in searching for the missing victims.

Thanh Hoa was hardest hit locality in Vietnam by storm Wipha which made landfall in the northern province of Quang Ninh last Friday night before weakening into a tropical depression and moving deeper inland, bringing heavy rain to northern and north central provinces.

The tropical depression weakened further into a low-pressure system as it moved to northern Laos.

The death toll from storm Wipha in Vietnam has climbed to 12 while nine others are still listed as missing.

15 people were swept away by a flash flood that hit Sa Na Village in Thanh Hoa last Saturday. Seven people have been confirmed dead.

Vietnam experiences a storm season between July and October. There were nine storms last year and four are expected this year.

Natural disasters, mostly floods, storms and landslides, killed 181 people last year and left 37 others missing and caused losses of around VND20 trillion ($858 million).