Tropical storm Wipha was set to cross Vietnam's northern coastline on Tuesday morning, with almost 350,000 soldiers on standby as the state weather agency forecast up to 50 cm (20 inches) of rainfall that could cause flooding and mudslides.

Typhoon Wipha has toppled trees and caused major flight disruptions in Hong Kong and at some nearby airports in China as it moved west off the country’s southern coast.

The thunderstorm came so suddenly that it overturned the boat within seconds, said two survivors of the shipwreck which killed at least 35 people in Vietnam's top tourist spot of Halong Bay and left another four missing.

Typhoon Wipha started building up over the South China Sea before hitting Hong Kong, Taiwan and China, and making its way towards Vietnam. Video credit: CSU/CIRA & JMA/JAXA

The death toll from a tourist boat accident in Vietnam’s Halong Bay climbed to at least 38 with several people still missing, the government said, as rescuers continued to search for survivors while bracing for the approach of Typhoon Wipha.

VOV.VN - Typhoon Wipha, packing powerful winds and torrential rains, is expected to move into the Gulf of Tonkin on July 21, and strike the northern coastal provinces of Vietnam within the coming hours,