Thousands of people from India's north-eastern states have fled the southern city of Bangalore amid fears that they will be targeted in attacks.
Indian Home Secretary RK Singh blamed the mass exodus on "rumour mongering".
He insisted there was was no threat to anyone from the north-east living anywhere in the country.
Correspondents say the rumours of attacks may be linked to clashes in the north-eastern state of Assam last month.
More than 300,000 people fled after fighting between indigenous Bodo tribes and Muslim settlers in Assam.
Fresh violence between the two sides was reported on Thursday when a mob burnt down a bus and a road bridge, reports say.
Police said local Muslims blocked a highway in protest against an overnight incident in which a group of Bodos set a car on fire near Rangiya, 60km (40 miles) west of Assam's main city of Guwahati.
The main railway station in Bangalore was flooded with migrant workers from north-eastern states after rumours spread on Wednesday.
The railways ran special trains to the north-east to cope with the rush, officials said.
There are 250,000 people from the north-east living and working in Bangalore, which is often referred to as the Silicon Valley of India.
Many of them are students, security guards and workers in the hospitality sector.
Around 4,000 fled on Wednesday, a senior police officer in the city told the BBC.
He said that rumours about possible violence were spread by text messages.
"We will soon catch hold of people who sent out these messages," said the police officer.
Karnataka Chief Minister Jagdish Shettar said that he had reassured Prime Minister Manmohan Singh that there were "no untoward incidents nor any threat to people of north-eastern states [living in Bangalore]."
He added: "I promised that [the] necessary steps would be taken to give protection to these people."
Manoj, a security guard from a north-east state, told the BBC that residents of the region were "all frightened".
"My friend [from the region] was threatened by a knife-wielding man saying that he should leave the city if he cared for his life," he said.
A worker at a city restaurant from the region said there were "rumours that people from the north-east would be attacked".
The rumours came a day after a 22-year-old Tibetan student was allegedly attacked in Mysore city near Bangalore by two people who suspected him of being from the north-east.
Many young people from the restive north-east region have migrated to the cities of Delhi, Mumbai and Bangalore in search of better jobs and education.