Wipha has remained steady but its winds are forecast to increase from 88 kph to 89-117 kph as it intensifies and hits the Gulf of Tonkin and Vietnam’s coast.

Vietnam is preparing for Typhoon Wipha, with emergency alerts in coastal provinces and flight cancellations. The typhoon threatens to bring severe weather, including heavy winds and floods, to northern mountainous regions and urban areas.

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.

Wipha, the third storm to hit Vietnam this year, is expected to bring torrential rains from tonight until Wednesday, particularly in the northeastern and central regions.

Storm Wipha is intensifying in the Gulf of Tonkin, threatening northern Vietnam with powerful winds and heavy rain.