According to the Do Son Border Guard Station, officers on patrol discovered the pod in waters about one nautical mile from Hon Dau Island.
Local authorities said the appearance of the dolphins was a positive sign reflecting improving marine environmental conditions in the Do Son area.
Dolphins are typically found in clean waters with rich marine ecosystems and are widely regarded in local culture as symbols of peace and good fortune.
Authorities in Do Son have stepped up efforts to improve the coastal environment, including tackling pollution and upgrading waste and wastewater treatment systems.
Under Haiphong’s tourism development plan through 2030 with a vision to 2045, the city aims to develop Do Son into a modern tourism hub linked with surrounding service and marine ecosystems.