The National Search and Rescue Commission is looking for 21 fishermen who are missing after their vessel sank in the southern province of Ba Ria Vung Tau.
One of the fisherman on the ship was found floating by another ship at around 4 p.m. on Saturday.
After he was resuscitated, he said that the boat, with 22 people on it, sank as it was fishing around 34 sea miles southeast of Con Dao Island.
The commission searched for the remaining fishermen throughout the night, but so far no one has been found.
The commission said it has also contacted foreign ships for help.
The exact cause of the sinking is still unknown.
Vietnamese officials were cited by the Tuoi Tre Newspaper as saying on Sunday that at least 49 Vietnamese vessels have sunk or been in trouble due to rough seas.