A disaster official says flash floods triggered by a tropical storm have killed seven people and left four others missing in a northern Vietnamese province.

Tran Viet Phuong in Son La province said Thursday that authorities are still searching for the four missing, including a four-year-old boy whose house was washed away.

Flash floods washed away more than 20 houses in the province, he said.

Tropical Storm Kujira which slammed northern coast on Wednesday has now dissipated, according to the national weather forecasters.

The storm has dumped up to 20 centimeters (nearly 8 inches) of rain on many parts of northern region over the past two days.

Vietnam is prone to flood s and storms, which kill hundreds of people each year.