Staff and soldiers at the Rong (dragon) oil field in the southern province Ba Ria-Vung Tau became the first people to vote for the National Assembly on Monday.
They also cast their votes for the provincial People's Council, the local legislative body.
Also on Monday two navy ships left Cam Ranh Port in the central province of Khanh Hoa for the Truong Sa (Spratly) archipelago, where legislative elections will start on May 15, five days before the elections start across the country.
Citizens are expected to vote for 500 members of the National Assembly, 3,200 members of People's Council at cities and provinces, and over 300,000 members of People's Council at districts and communes.
Elections of the National Assembly and the People's Council happen once every five years, but they are usually scheduled two years apart. However, this time the elections have been organized at the same time.