Both the Chinese boats opened up with .50-caliber machine guns.
Vietnam says the Chinese boats deliberately cut the survey ship's cables in Vietnamese waters.
The explosion caused the Chinese boat to split in half after both sides had filled with water.
They said they had been told the fishermen were rescued by another Chinese boat.
An owner of one of the hijacked ships stated that almost every Chinese boat in the area had been robbed by river gangs.
A Chinese boat is tattooed on one leg, and a dragoon looks from the other.
The class is larger than its predecessor and is the most widely built and exported Chinese military boat in terms of numbers.
Chinese boat takes the lead with a massive 150 mile advantage, but ahead lies a tropical depression which could deliver 50 knot headwinds.
Former Soviet or Chinese boats have been retired from service.
In April 2012, the Philippines accused Chinese boats of fishing illegally.