Robin Justin Williams, 50, was swimming with a group of five males and four females of different nationalities at the Tam Thanh Beach in Tam Ky Town when the waves swept him away.
The group arrived at the beach after cycling more than 40 kilometers (25 miles) from the ancient town of Hoi An with help from a Vietnamese tour guide.
Members of the group reported Williams missing to the beach rescue team right after the incident happened, but so far, there has been no sign of him. Big sea waves are said to have made things difficult for rescuers.
UPDATE: His body was found washed ashore on Monday morning, two kilometers from where he was swept away.
Tam Thanh Beach lies eight kilometers from Tam Ky and is usually deserted this time of year, because the water is cold.
In the first half of this year, Quang Nam attracted more than four million visitors, up 17 percent against the same period last year, including 2.5 million foreigners, up 24 percent.