Police in Quang Ninh Province said they had arrested the captain and a crew member of a tourist boat for stealing from a foreign tourist, news website VnExpress reported.
Nguyen Dang Trieu, 29, skippered the Truong Giang tourist boat with 18 foreign tourists onboard on Ha Long Bay last Friday.
One of the tourists then reported his bag was lost.
After a search was conducted, the tour guide found the bag under a passenger seat, but more than US$378 in cash inside the bag was missing.
After Trieu, Vu Ba Tien, the boat owner, and Bui Huy Thanh, the 21-year-old sailor, all claimed they were not aware of the money, the tour guide decided to call police.
While being questioned by the police, Thanh tried to bribe them VND2.4 million ($112). The police officers made a report on the bribery.
He and Trieu then confessed to police they had connived to steal the bag.
They also confessed they had stolen from another foreign tourist on the same boat on March 8.