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.

Vietnam braced for Typhoon Wipha on Monday as coastal provinces were placed on emergency alert and airlines canceled flights ahead of the storm’s expected landfall early Tuesday.

The typhoon is forecast to bring powerful winds and heavy rainfall, raising the risk of flash floods and landslides in northern Vietnam’s mountainous areas and flooding in urban centers, including Ha...