Tens of thousands of spectators thronged the riverfront in the Cambodian capital Phnom Penh Sunday for an annual dragon boat race -- the centrepiece of the kingdom's three-day water festival, cancelled during the COVID pandemic.

Around 300 boats, their crews dressed in matching bright T-shirts, strained for the win as they dipped their colourful paddles into the Tonle Sap river with the royal palace behind them.

Cambodian King Norodom Sihamoni, Prime Minister Hun Manet, his father Hun Sen and senior government officials looked on as the yearly extravaganza began, with crowds urging the canoes over the final line.

Concerts, parades of lantern floats bedecked with colourful neon lights -- each representing a government ministry -- and fireworks are all part of the three-day festival that will last until Tuesday.

"I am happy that we can meet to celebrate the water festival," 38-year-old rower Hom Phos told AFP.

"I am so excited because it is our national festival."

The festival was last held in 2019, after which it was halted during the pandemic.

"During the COVID pandemic, everyone was worried about it, and we were not happy. But now we are happy again," fellow rower Yorn Vorn, 45, told AFP.

The festival marks the end of the rainy season when the Tonle Sap river, which joins the mighty Mekong River in front of the Royal Palace, reverses flow. 

Health authorities are also expected to distribute 80,000 condoms and 20,000 packages of lubricants for free to oarsmen and visitors during the festival to raise awareness about HIV and AIDS prevention.

The celebrations turned deadly on the last day of the festival in 2010, when more than 350 people were killed in a stampede on an overcrowded bridge after panic spread over rumours it was about to collapse.

Then Prime Minister Hun Sen described the disaster as Cambodia's worst tragedy since the Khmer Rouge's 1975-1979 reign of terror, which killed up to a quarter of the population.