At least 38 people were killed and several remain missing after a tourist boat capsized during a sudden thunderstorm in Vietnam’s Ha Long Bay on Saturday afternoon.

Authorities confirmed that 12 people were rescued from the wreck, while search efforts continue for seven others.

The vessel, identified as the Wonder Sea, was carrying 48 passengers and five crew members on a sightseeing tour of Ha Long Bay, one of Vietnam’s most popular tourist destinations.

According to state media, the boat overturned due to strong winds and rough waters brought on by an unexpected thunderstorm.