MNS supporters are alleged to have gone on the rampage
Three people were killed during rioting on Tuesday night in the Indian state of Maharashtra, police say.
The rioting followed the arrest of Raj Thackeray, the leader of the right-wing Maharashtra Navnirman Sena (MNS) party.
Mr Thackeray is accused of inciting violence against migrant workers. He obtained bail on Wednesday.
Meanwhile, students in the state of Bihar have paralysed rail services in protest at the ill-treatment they say Biharis have received from the MNS.
Maharashtra police chief AN Roy told the AFP news agency that the three deaths took place in clashes between supporters of the MNS and "outsiders" near the town of Kalyan, north-east of Mumbai (Bombay).
Mr Thackeray says jobs should be given to locals
Mr Roy said that a "large" number of police had been deployed to maintain order and he was confident they could contain the violence.
"We have made all preparations," he said.
On Tuesday hundreds of Mr Thackeray's slogan-shouting supporters fought pitched battles with police for hours, causing large-scale disruption in Mumbai.
Taxis and buses were destroyed and more than 500 people detained.
MNS supporters demanded the unconditional release of their leader, who was woken up from his sleep and arrested early on Tuesday morning in a town 400km (250 miles) from Mumbai, where he had lined up a series of public meetings.
He was charged with rioting, preventing government employees from performing their duty and damaging property.
On Wednesday, Mr Thackeray reappeared in court in Kalyan amid tight security and was granted bail.
"He is now a free man. He can go home," a lawyer representing him told reporters.
The court banned Mr Thackeray from speaking in public or talking to the media.
The MNS has been accused of several attacks on migrant workers in recent months.
The protesters say there are too many migrant workers in Maharashtra
Many of them come from Bihar, where rampaging students set fire to coaches of the South Bihar Express at Barh railway station in the state capital, Patna.
The students threw stones, smashed computers, window panes and furniture as part of their protest against Mr Thackeray.
The BBC's Amarnath Tewary in Patna says that police fired in the air to disperse the mob.
Five students were arrested but police say that no one was hurt in the incident.
Our correspondent says protesters stopped trains in many other places and vandalised railway stations.
The Bihar chief minister has now initiated talks with the students in an effort to lower tensions.
The unrest in Maharashtra has forced many migrants to leave their neighbourhoods, but Mr Thackeray has consistently denied inciting it.