Workers building a large factory for Samsung in northern Vietnam have fought with security guards and set fire to motorbikes.
State media reports said the unrest on Thursday following an argument between a guard and a worker who turned up late at the complex.
Local official Duong Ngoc Long said police restored order after three hours.
Video posted on YouTube showed workers throwing rocks at police in riot gear as thick black smoke rose from parts of the complex.
Mr. Long said four people were injured.
Samsung and other tech companies are increasingly moving factories to Vietnam, where labour costs are cheaper than in neighbouring China.
Around 10,000 workers are building the Samsung plant in Thai Nguyen province.