India's technology hub of Bengaluru deployed riot police on Monday to rein in protests as a water dispute turned violent, with cars and buses set of fire and people pelted with stones.
Television footage showed flames pouring from burnt-out vehicles as angry crowds gathered nearby, while police said the local metro network had been temporarily suspended.
The violence erupted after India's Supreme Court ordered Karnataka state, where Bengaluru is based, to release 12,000 cubic feet of water per second every day from the Cauvery river to neighboring Tamil Nadu.
The river has been the source of more than a century of tension between the states, and the anger has previously turned violent - in 1991 an interim court order telling Karnataka to release water to Tamil Nadu sparked riots against Tamils in Bengaluru, leaving more than 18 people dead.
"Rapid Action Force Teams have been deployed all over the city," Bengaluru city police said on Twitter on Monday. "We urge to all Bengalurians...Stay calm and not to be panic."
A Reuters witness saw a group of 20 to 30 protesters, some armed with sticks and stones, stopping and searching cars.
They pulled several Tamil Nadu-registered trucks and motorcycles to the side of the road and pelted them with stones. At least one truck driver was beaten with a stick. The protesters let Karnataka-registered vehicles through the makeshift roadblock.
Police said that more than 15,000 officers had been deployed to keep the peace including riot police and border security forces. They denied media reports that forces had imposed prohibitory orders on crowds gathering in public places.
Bengaluru is home to top Indian IT companies such as Infosys Ltd, Wipro Ltd and Mphasis as well has offices of several multinational companies like Samsung Electronics.
Media reported a small number of attacks on Tamil-owned property in Karnataka, while the Karnataka chief minister said on Twitter that he had asked his Tamil Nadu counterpart to investigate reports of violence in Tamil Nadu against people originally from his state.
Disputes over water resources are common in India, where rising demand and poor management of supplies often leads to angry protests.