The incident took place late on February 18, and details of when the cable will be fixed have not been provided.
This is the second time that the Asia America Gateway (AAG) has been disrupted this year following several ruptures last year.
The latest repair work on the AAG was only completed in late January after it cut off on January 8.
This new disruption was triggered by a problem on the cable between Vietnam and Hong Kong.
In early January, the AAG and two other internet cables, the Intra Asia (IA) and the newly launched Asia Pacific Gateway (APG), all experienced problems and were subsequently shut down.
The APG was back up on January 23 while the IA is expected to be fixed by February 25, VietnamPlus quoted service provider Viettel as saying on February 19.
The AAG is well known to internet users in Vietnam for its frequent ruptures, which even inspired internet memes to blame the issues on "sharks".
In 2016 alone, it ruptured three times, heavily affecting outbound traffic.
Vietnam has five submarine cable systems. The AAG was connected in November 2009 with a length of over 20,000 kilometers and a design capacity of 2 terabits/second, directly connecting Southeast Asia with America.
The other main connection is the APG Submarine Cable which was hooked up in late December and was officially launched on January 3.
The cable cost US$450 million and has a design capacity of more than 54 terabits/second.
In addition to submarine cable systems, Vietnam has a land-based system with a capacity of 120 gigabit/second that goes through China, and there are plans to build another one.