Around 20 people were injured in the quake-hit region of China's southwestern Sichuan province following clashes with police over a proposed chemical plant, protesters and officials said.
Separately, riot police dispersed a protest by parents who lost their children in the devastating 2008 earthquake, they said.
"We have been terribly treated here," said an eyewitness surnamed Chen from the quake-hit town of Mianzhu, which has already seen clashes between police and parents whose children were killed under collapsed school buildings during the devastating May 12 earthquake.
"They have been beating us up and detaining us today," Chen said. "There were about 200-300 police vehicles here today."
He said the riot police forced the villagers to abandon a sit-in at the proposed site for a chemical plant in protest at the sale of their land for the project, for which they say they have received no compensation.
"There must have been at least 1,000 of them, and we were only a small group of about 200 to 300 people," Chen added.
A second villager at the scene said he saw around 20 people injured during the clashes.
"They have detained at least 10 people, men and women," he said. "I think there were about 700 or 800 police who came."
"They were all military personnel with riot shields and police batons," he added.
He said some of those injured were elderly people in their sixties and seventies.
"They were taken to hospital after they were beaten," he added.
The reports were confirmed by one doctor at the local hospital.
"At first there were only two injured people, and then after that there were some more," the doctor said.
"The injured are being sent to the Mianzhu People's Hospital. We don't really know any of the details."
An official who answered the phone at the Mianzhu municipal government offices said he had not heard the news of the clashes, which local residents said happened at the chemical plant under construction in Gongxing township.
"We haven't received any bulletins about this," the official said. "We don't know about this."
But the Gongxing local government said it had already sent officials to the scene.
"Our government officials are there, dealing with this matter," said an employee who answered the phone at the Gongxing township government offices. "They've gone to the scene, I believe."
A third villager said the clashes had been sparked by a dispute over the sale of land used for the chemical plant.
"We want to tell them that if they are going to requisition our land, then they should pay us some compensation," he said.
"That's why local people won't let them start work on the construction site."
"They came in and started detaining people and beating them up."
He said around 20 people had been injured and taken away by police.
"They have been taken to hospital," he said.
He said the dispute was around a 500-mu (82-acre) plot of land that was sold to the developer by the local government.
"They never compensated us or subsidized us," he said. "They said we couldn't prove it, so this is the only option we have left."
"We are trying to protect our rights."
Elsewhere in Sichuan, police detained parents of children killed in the earthquake after they tried to meet with the mayor of Deyang city to discuss compensation claims on Monday.
Around 80 parents from the surrounding countryside traveled to the city to support the petition, only to be met by around 100 riot police, a bereaved parent surnamed Li said.
"The police divided up the group of parents, and ... detained some of them," Li said. "The rest were told to scatter by the police, and left the scene."
"There were a lot of police in those vehicles," he said. "There were a dozen or so police to each person they detained."
"Everyone scattered," he added.
A parent surnamed Fan said he had left the scene after police arrived. "There were a lot of police, and we didn't want trouble, so we left," he said.
"They saw there were a lot of us, and they warned us not to go through with the petition, and that we could go to jail if we carried on making a fuss."
Another woman said the police response was similar whenever the parents tried to protest.
"They always detain one or two people," she said. "They are trying to frighten us, and suppress us, and bully the people."
Parents who lost children when school buildings collapsed in the earthquake have called for an inquiry into alleged shoddy construction, amid continuing official pressure and warnings not to talk to foreign media.
Parents from worst-hit Dujiangyan have also said they are being followed, threatened, and prevented from lodging official complaints in Beijing and with higher authorities.
Sichuan authorities have already jailed one activist, writer Tan Zuoren, after he carried out an independent investigation into the children’s deaths and published it online.
Chinese officials report thousands of "mass incidents" across the country every year, many of which are protests or sit-ins linked to forced evictions, allegations of corruption, and disputes over rural land sales.
Reported by Qiao Long for RFA's Mandarin service and by Hai Nan for the Cantonese service. Translated and written in English by Luisetta Mudie.