Floods and landslides in northern Vietnam have killed at least 30 people over the weekend, Vietnamese television has reported.
Bac Kan province was the worst hit, with other casualties reported in Cao Bang, Ha Giang and Lai Chau provinces.
In southern China, flooding has left at least 20 people dead, state media said.
It said more than 300,000 people had been forced to leave their homes, and up to 10m people were affected by seasonal flooding.
In Vietnam, television showed many houses flooded to their roofs and warned of a "high" risk of a sudden rise in flood levels across several districts.
Heavy rains have been reported in northern Vietnam since late on Friday, swelling local rivers and streams.
Landslides and floods cut off roads, telecommunications and power supply in some areas, and fields of rice, corn and cassava were damaged, the government's disaster report said.
Vietnam is often struck by floods and storms between July and October.
China battered
The casualties and property damage in the Vietnamese area bordering China emerged after torrential rain hit southern China and displaced hundreds of thousands of people.
The China Daily newspaper said rainstorms that lasted for three days killed about 20 people and affected millions.
Houses were toppled, roads flooded, and crops damaged in the Guangxi Zhuang autonomous region and the nearby provinces of Fujian, Guangdong and Jiangxi, Xinhua News Agency reported.
In Liuzhou, the region's second largest city and an important transportation hub, water resources authorities called the flooding "the third biggest in history".
"These rains always come and go here; there's only so much you can really do," Liu Junjie, a spokesman for Liuzhou's flood control and drought relief headquarters, told China Daily.
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