Cambodia may be suffering the worst drought for half a century but a ritual involving royal oxen on Tuesday nevertheless predicted a bountiful harvest this year.

The ploughing ceremony, presided over by King Norodom Sihamoni, was held at the famed Angkor temple complex in the northwestern province of Siem Reap.

Thousands of locals and tourists gathered to observe the ancient rite, which marks the start of the harvest season.

After the symbolic ploughing of a portion of the field, a pair of decorated oxen were led over to seven dishes containing food or drink and laid out on trays.

The dishes of rice, corn, beans and sesame represent the harvest, and the more the oxen eat, the better it is expected to be.

However if the beasts choose the offerings of grass, water or alcohol, it suggests illness, floods or war are on the way.

The oxen ate most of the rice, beans and corn, prompting the palace's chief astrologer Kang Ken to declare to a crowd that those crops would see "bountiful harvests".

The astrologer did however warn it was "just a prediction".

He then appealed to holy spirits to bless the country with regular rain so that "the kingdom of Cambodia avoids any natural disaster that would affect agricultural products, which are the life of the people and the nation".

The Greater Mekong region was scorched by an unusually hot dry season this year, with temperatures regularly hitting 40C (104 Fahrenheit).

Cambodian officials said the country was suffering the worst drought in 50 years, forcing authorities to assist 18 out of 25 provinces with water supply.

Some 2.5 million people were affected by the dry spell, which also led to the deaths of cattle, monkeys and tonnes of fish, according to officials.

Despite the royal oxen's prophecy, a spokesman for Cambodia's disaster management centre said he expected a weaker agricultural yield this year.

"Due to bad weather, I think the harvests this year will be reduced," Keo Vy told AFP, explaining that farmers across the country have delayed planting rice -- an irrigation-intensive crop -- due to the drought.

"Rice exporters have voiced concerns there would won't be enough milled rice for export," he added.