Demonstrators are reported to have thrown rocks and taken three officials hostage. Witnesses said the police used batons to beat back a crowd of hundreds who gathered at a local government office to demand the release of fellow protesters.
The flare-up in Quang Ngai province follows sporadic clashes over the last two years in provinces further north over a toxic leak that damaged the livelihood of fishing communities.
The protests began when villagers in Pho Thanh commune began blocking roads leading to a new waste disposal facility that they said was too close to their homes.
The provincial authorities agreed to suspend operations at the plant in July, but infuriated protesters rushed to the government office last Sunday night following reports that work had restarted at the plant.
Thirty were arrested by police in the subsequent melee.
Further clashes occurred on Tuesday when a crowd turned up to demand their release.
The protesters are reported to have taken three officials hostage during the confrontation, but later released them.
The police said they had released most of those arrested on Sunday but were continuing investigations against nine.
The breakdown in talks and resort to violence underlines the lack of trust between officials and local people, a pattern repeated in similar disputes across the country.
The citizens of Pho Thanh believed they were being deceived by the local authorities and appear to have made their feelings known as directly as they could.