The 10-year-old was on a trip with his family in Vietnam’s renowned Ha Long Bay when the boat they were on was unexpectedly caught in a severe storm. As the boat overturned, the boy found a small air pocket underwater, where he took shelter, waiting for rescue operations.

Rescue teams were eventually able to locate him in relatively good physical condition, though he was experiencing emotional trauma. He was warmed up and taken to a nearby hospital, according to local news source VietnamNet.

He said that the boat quickly filled with water and he lost all orientation.

“I tried to breathe, but more water was coming in. I took a deep breath, removed my life jacket, and dove deeper. I noticed a glimmer of light and swam towards it to escape the boat, then climbed onto the overturned vessel to seek help,” he recounted.

Tuan, along with several others who had been on board, clung onto the overturned boat and waited for another two hours in pouring rain until emergency crews arrived.

He’d been holidaying in Vietnam’s popular tourist bay with 11 university friends. Only three of their group survived.

VN Express reported that the Wonder Sea was caught in a storm around 1:30pm local time (4:30pm AEST), which caused it to capsize.

Most of the passengers were from the Vietnamese capital Hanoi and travelling as families, according to VN Express, which reported the eldest passenger as 53 years old and the youngest as just 3.

Over 20 children were on board, VNExpress said.

The capsize reportedly happened near the Dau Go Cave – one of the largest in the bay.

Halong Bay is a popular tourist hotspot and a UNESCO world heritage site comprising about 1600 limestone islands and islets.