Vietnam set off a spectacle of lights, dance and music at Thursday's opening ceremony of the Southeast Asian Games, brushing aside gloomy weather to launch a party-like atmosphere eclipsing a six-month Covid delay of the event.

Fireworks exploded above the capital city's 40,000-seat My Dinh National Stadium during the two-hour show, as colourful computer-generated landscapes and traditional art were projected on a giant screen and white stage.

The 18-day biennial SEA Games has Olympic staples including athletics and swimming alongside regional sports like the Indonesian martial art of pencak silat and xiangqi, also known as Chinese chess.

Hundreds of athletes representing the over 4,900 sportsmen and women from 11 competing nations strolled from behind the screen, waving national flags as they walked past lines of women in traditional Vietnamese dress.

"On behalf of the leaders of Vietnamese party, state and government, thank you for participating in the opening of the 31st SEA Games in Hanoi," Vietnam's President Nguyen Xuan Phuc said in a speech.

"I declare the opening of the Games, and wish the Games a big success."

The region's top leaders were not present at the opening ceremony, as Southeast Asia's heads of state were in Washington meeting with US President Joe Biden at a special summit.

Filling their place instead were senior Vietnamese leaders and regional sports officials.

The Games were originally planned for a November 2021 launch but were postponed by six months after a fierce Covid-19 wave infected millions and locked down the country.

It has been nearly two decades since the communist country first hosted the Games in 2003, and the second time the stadium held the multi-sports event's opening ceremony.

A short but heavy mid-afternoon downpour initially drenched the stadium though it failed to halt hundreds of dancers moving to the music and the projected images.

Hot air balloons bearing the competing nations' flags rose above the stadium, and a Vietnamese runner, Quach Thi Lan, lit the torch for the Games.

As the ceremony ended local pop singers belted the Games' official song, "Let's Shine," with the audience using their mobile phone flashes to illuminate the stadium in a sea of lights.

Competition has already started and finished in some events, including beach handball, kickboxing and diving, the last of which Malaysia dominated with a clean sweep of the sport's eight categories.

Ahead of Thursday's ceremony, Vietnam made a strong start with 10 golds, with Malaysia closely behind with nine along with Indonesia's three.

But the bulk of the disciplines begin Friday and run until the closing ceremony on May 23.