Tourists joined nearly 3,000 professional and amateur performers at the Bai Chay tourist site during a public street party.
The festival opened with a special music performance with the participation of famous singers from many countries.
More than 100 decorated boats created a splendid scene in the harbour; there was a Samba dance staged by over 500 dancers; a laser, sound and water performance lasting up to 90 minutes; and a closing fireworks display.
Cultural events during the festival include a poetry-music show, a competition for MCs, culinary festival, tennis tournament, bonsai exhibition and a cock fight festival.
Director of the provincipal Department of Culture, Sports and Tourism Ha Quang Long said the carnival was even more important than usual with the vote for UNESCO's World Heritage Site Ha Long Bay as one of the world's New Seven Wonders looming in November.
The bay is second in the poll behind South Korea's Jeju Island. In total, there are 28 finalists on the New Wonders list.
The provincial authorities invested more than VND138 billion (US$6.57 million) in preparations for the festival.