PHNOM PENH (AFP) - Cambodian police arrested dozens of garment workers Monday (Dec 21), breaking up a pay protest with water cannon at a factory site near the Vietnamese border, unions and a local governor said.

Labour disputes beset the country's multi-billion dollar garment industry, which supplies big global brands including Gap, Nike and H&M, often resulting in strikes and heavy-handed crackdowns by authorities.

Hundreds of police and military police were deployed at the Special Economic Zone in the town of Bavet in Svay Rieng province, after around 8,000 workers protested against a low pay rise.

They had been promised a salary rise of US$20 (S$28) a month but were awarded only US$10, according to Chea Udom of the Collective Union Movement of Workers.

Security forces moved in after workers hurled rocks, using water cannon mounted on fire trucks to disperse the protest, he added.

Chea Udom said "more than 30 people" were arrested by police who "put them on the trucks and drove off quickly", adding that women were among those detained.

The governor of Bavet, who led the crackdown, said the situation had to be brought under control after days of snowballing protests.

"We have tolerated them for a long time already," Governor Seng Sila said of the protesters.

"Our forces are only protecting the factory, its investors and the safety of the workers." The workers did not put forward a representative for negotiations, he said, adding that staff from one factory started throwing rocks at other employees who had not joined their protest.

About 700,000 workers provide the backbone of Cambodia's garment industry, a key source of export earnings for the impoverished kingdom.

Last month Cambodia said it would raise the minimum monthly wage for garment workers to US$140 from January, an increase of nearly 10 per cent, but which fell short of union demands.