Vietnam has again vowed to crack down on tour boat safety after foreign visitors had a lucky escape from their sinking vessel, in an eerie echo of a fatal accident earlier this year.
There were no injuries in the latest incident, which involved 28 French tourists on Sunday afternoon at the popular attraction of Ha Long Bay.
Local authorities have taken "very active measures to investigate and review" what happened, Ministry of Foreign Affairs spokeswoman Nguyen Phuong Nga told reporters.
"We will conduct very close monitoring and supervision activities to avoid any further events taking place in the future," she said.
According to Dang Huy Hau, vice chairman of the People's Committee of Quang Ninh province, the boat went down after a collision with another craft delivering water.
But the French tour group leader, Josette Farret, told AFP there was "absolutely no collision".
The tourists were transferred to another boat before it completely sank, Hau said.
Authorities have suspended operations of Hai Long Co Ltd, the boat operator, while they investigate, the official Vietnam News reported.
In Vietnam's worst tourism accident, 11 tourists and their guide died in February when a boat sank in Ha Long Bay, a UNESCO World Heritage site known for its stunning limestone cliffs, about 160 kilometers (100 miles) from Hanoi.
A senior provincial official said water leakage resulting from human error was the most likely cause of that incident.
The boat's captain and engineer were arrested for investigation over alleged safety violations, which prompted authorities to carry out a safety inspection of 135 boats in the Ha Long Bay tour fleet.