Mobs burnt Tamil Nadu-registered trucks and buses on the roads and vandalized shops in the city. An NDTV team saw about two dozen buses being set on fire at a bus depot around 17 km from Bengaluru. "We will give blood but not Cauvery," screamed slogan shouting protesters.

The state's Congress government and the police appeared to be severely challenged by the scale of protests and the damage to public property. Images showed young men turning over an Innova car and wrecking it using rods, and throwing stones at shops. The Supreme Court had earlier said on protests in Karnataka: "Citizens cannot become a law unto themselves."

In the evening, large gatherings were banned in Bengaluru as a precaution. Most schools and colleges and some offices were closed early and metro services were briefly stopped.

The court had this morning modified an earlier order and said Karnataka has to release less water to Tamil Nadu, but for five more days. Karnataka, which will end up giving more water, urged a review but the court refused.

Thousands of policemen, including those in riot gear, spread out across the city to check violence. The centre also rushed ten companies comprising 1,000 personnel of the special anti-riot paramilitary force RAF to Karnataka. Karnataka stopped buses from heading to Tamil Nadu and police jeeps were positioned along the border to warn vehicles against entering that state.

There were protests also in Tamil Nadu. The New Woodlands hotel in Chennai, owned by a Karnataka company, was vandalised by a fringe group that allegedly also threw a petrol bomb and left pamphlets warning of retaliation if Tamils were targeted in Karnataka. Four of 10 attackers have been arrested. Five tourist vehicles from Karnataka, including two buses, were damaged by protesters in Rameswaram in southern Tamil Nadu.

Karnataka Chief Minister Siddaramaiah, in a letter to his Tamil Nadu counterpart Jayalalithaa, urged her to take action against those involved in violence against Kannada speaking people in her state. He also said the attack on a young man in Bengaluru was "blown out of proportion".

The man - reported to be Tamil - was attacked and humiliated in Bengaluru on Saturday by a group allegedly over his comments on social media on the Cauvery dispute. In a video of the attack that went viral, the engineering student was slapped and kicked by the men. The police suspect he was attacked after his post on Facebook mocking Kannada actors was widely circulated.

Ms Jayalalithaa too wrote to Mr Siddaramaiah on Monday evening, seeking protection for Tamil speaking people and their property. Home Minister Rajnath Singh also called up Chief Ministers of Karnataka and Tamil Nadu and assured them all central assistance in handling the law and order situation.