Witnesses say security personnel are manning roadblocks and patrolling the streets, and have ordered people to stay in their homes overnight.
No violent incidents were reported on Monday night.
Hundreds of workers rioted at the weekend after a  pregnant woman was allegedly assaulted by security guards.
Reports said the woman was shoved to the ground when she refused to move her market stall.
The protesters set fire to cars and damaged government buildings in Zengcheng, near the wealthy southern city of Guangzhou.
Police reportedly fired tear gas and deployed armoured vehicles.
A migrant worker from Sichuan who works in the area told Reuters news agency that people were angry with the system.
"I feel the rule of law here doesn't seem to exist... the local officials can do what they want," he said.
Some residents told the Associated Press they had been told not to go out at night or post photos of the unrest online.
"Nobody wants to come out. They fear running into danger," one factory worker told AP.
Complaints about corruption and abuse of power are widespread, especially among migrant workers who are often paid meagre wages.
Zengcheng has a booming garments industry, and its 800,000-strong population has been boosted by thousands of migrant workers in recent years - many of whom come from Sichuan province.
Chinese security forces have moved into the southern city of Zengcheng, restoring calm after days of rioting by migrant workers.