Three Chinese policemen went on trial Monday over the fatal beating of a female migrant worker, state media said, a case that sparked an online outcry about violence by law enforcers.

Zhou Xiuyun, 47, was assaulted by the police at a construction site in Taiyuan in December as she tried to prevent officers taking away her husband and son over a dispute with security guards, according to previous media reports.

The three were taken to a local police station where Zhou was thrown to the ground while the two men were beaten up, they said. Zhou died the next day in hospital.

Footage showing policeman Wang Wenjun trampling the hair of a dazed Zhou went viral online a week later, intensifying public anger.

Wang went on trial for intentional injury and abuse of power on Monday in Taiyuan, the capital of the northern province of Shanxi, state broadcaster China Central Television reported.

His colleagues Guo Tiewei, who was charged with abuse of power, and Ren Haibo, who faces a charge of intentional injury, joined him in the dock, it said.

Police in China are accused by rights groups and critics of aiding companies or local governments in cases such as labour disputes, land seizures and evictions.

They often use violence to extort confessions, according to human rights activists, while abuses by urban management officers known as "chengguan" also regularly trigger public fury.

Earlier this month a police officer shot dead a man who scuffled with him and hit him with a baton at a train station in the northeastern province of Heilongjiang.

In 2013 a farmer in the central province of Hunan was beaten to death by six chengguan for selling watermelons at a street stall without a licence.