HA LONG BAY, Vietnam — A tourist boat capsized during a sudden thunderstorm in Vietnam on Saturday afternoon during a sightseeing excursion, killing 18 people and leaving nearly two dozen others missing, state media reported.

The Wonder Sea boat was carrying 48 passengers and five crew members during the tour of Ha Long Bay, a popular destination for visitors, according to the reports.

Rescue workers saved 12 people, and recovered the 18 bodies near the site of the capsizing, VNExpress newspaper said. Twenty-three people remain missing.

The boat turned upside down because of strong winds, the newspaper said. A 14-year-old boy was among the survivors, and he was rescued four hours after being trapped in the overturned hull.

The newspaper said that most of the passengers were tourists, including about 20 children, from Hanoi, the country’s capital.

A tropical storm is also moving toward the area. A national weather forecast said that Storm Wipha is expected to hit Vietnam’s northern region, including Ha Long Bay’s coast next week.