HANOI, Vietnam (AP) — Workers building a massive Samsung factory in northern Vietnam battled police and torched motorbikes on Thursday, in a rare outbreak of labor violence in the tightly controlled country.

Samsung and other tech companies such as Intel and Nokia are increasingly moving production to Vietnam, where labor costs are cheaper than in neighboring China. The country’s Communist rulers are encouraging them with tax breaks, eager to move away from traditional exports of clothes, shoes and shrimps to higher value products

The riot at the Samsung complex in northern Vietnam, footage of which was taken by bystanders and posted on YouTube within hours of it breaking out, will concern authorities and tech company executives alike.

State media reports said the unrest followed an argument and ensuing fight between a guard and a worker who turned up late at the complex, where up to 10,000 people are currently employed.

Motorbikes and containers housing security guards were set alight, sending thick smoke over the complex. Footage showed people throwing rocks at police in riot gear who huddled together. Local official Duong Ngoc Long said police restored order after three hours. Four people were injured, he said.

Vietnam’s tech exports, mostly phones and tablets assembled from parts made in China and elsewhere, increased sharply over the last three years, but the country’s trade remains dominated by less sophisticated products.

Samsung is making the country of 80 million people a major manufacturing base for its smartphones.

Construction of the $2 billion plant in Thai Nguyen province began last year. When complete, it will reportedly be company’s largest production facility in the world.