Police say about 5,000 people attended the protests
Nine people were killed in clashes with police in the southern Indian state of Tamil Nadu amid protests against copper smelter that residents say is causing environmental damage.
The protests against Sterlite Copper subsidiaries of the Vedanta conglomerate have been going on for months in the port city of Tuticorin.
Police said the clashes erupted when a large crowd of protesters stormed the district government headquarters.
Many others were seriously injured.
Police said the crowd began throwing stones at police and office buildings, toppling cars and burning vehicles.
They say they opened fire when violence intensified.
A state minister defended police action, saying that it was "unavoidable".
Protesters overthrow vehicles and burn public property
"Entering the office and violence is unacceptable ... shooting [opening fire] becomes unavoidable," fisheries minister D Jayakumar told reporters in Chennai, formerly known as Madras. He said nearly 3,000 troops had been taken from the neighboring district to control the situation.
Protesters say the plant pollutes groundwater in the area and threatens the fishing industry.
The plant has been closed for more than 50 days due to alleged non-compliance with environmental regulations.
Vedanta denies all charges against him and says plans to double factory capacity. The company has not commented on the violence on Tuesday.