Tensions in southern China between police and migrant workers from other provinces appear to be escalating.
Migrant workers clashed with police on Monday for a third consecutive night outside the southern city of Guangzhou.
About 1000 protesters set fire to cars and damaged government buildings near the city.
Police reportedly fired tear gas and deployed armoured vehicles.
The protests began over reports of mistreatment of a pregnant migrant worker by security guards.
Witnesses said she fell to the ground - some say she was pushed - after a disagreement with security officials, who wanted her to move her stall from in front of a supermarket.
The BBC says that when news of the incident spread, other migrant workers - most from Sichuan province - went on the rampage.
Bricks and bottles were thrown, windows were smashed and police vehicles were overturned. At least 25 people have been arrested.
Zengcheng - just outside Guangzhou - is a hub for clothing factories and is home to migrants working in a number of textile factories.
Corruption complaints common
The BBC reports that complaints about corruption and abuse of power are widespread and incidents like this happen across China every week.
The arrests followed a separate incident further north, in Lichuan city in Hubei province, where hundreds of people laid siege to local government offices following the death in custody of a respected official.
Ran Jinxian was arrested for allegedly taking bribes linked to land seizures and forced demolitions of people's homes.
Mr Ran, 49, was arrested on 26 May and died on 4 June. His family said he was beaten to death during interrogation.
Several officials have been detained or are under investigation over Mr Ran's death.