A tourist boat in Vietnam capsized on Saturday, leaving 35 people dead and several others missing, according to authorities.

The vessel was carrying 53 people, when it capsized while doing a tour of northern Vietnam's famous Ha Long Bay. Most of the passengers were tourists from the capital Hanoi, local media said.

Border guards had recovered dozens of bodies on Saturday and another three crew members' bodies were recovered by Sunday morning. Efforts were still on to find the missing people. 

"I took a deep breath, swam through a gap, dived then swam up, I even shouted for help, then I was pulled up by a boat with soldiers on," a rescued 10-year-old boy told state media outlet VietnamNet. 

Authorities are trying to determine the cause of the accident and see if there were any safety violations.

Ha Long Bay is a UNESCO World Heritage Site, which spans over 1,500 square kilometers (579 square miles).

It is filled with nearly 2,000 islands and islets and is considered one of Vietnam's most popular tourist destinations, attracting millions of visitors each year.

What happened to the boat?

The vessel, dubbed Wonder Sea, was carrying 48 tourists and five crew members at the time of the capsizing, including families with children, VNExpress news outlet reported.

Sudden stormy weather landed in Ha Long Bay, with heavy rain and strong winds that appear to have caused the Wonder Sea to overturn.

There were "hailstones as big as toes with torrential rain, thunderstorm and lightning," Ha Long Bay office worker Tran Trong Hung told the French AFP news agency.

What do we know about the victims?

Rescuers recovered 35 bodies on site. Some 11 people were rescued, while seven are still missing.

Among those confirmed dead were eight children, VNExpress reported.

The news outlet said a 14-year-old boy was among the survivors. He was rescued four hours after being trapped in the overturned hull.

Authorities would "investigate and clarify the cause of the incident and strictly handle violations," a statement on the government website said.

Rescue efforts were set to continue into the night to find the missing.

Edited by: Rana Taha, Wesley Dockery