A passenger was injured in the firing
A number of senior Indian politicians have protested against the killing of a migrant job seeker by police in the city of Mumbai (Bombay).
Police said Rahul Raj, from Bihar, shot and injured a bus passenger as he tried to hijack the vehicle, demanding to meet local politician Raj Thackeray.
Mr Thackeray has been accused of inciting violence against migrants.
Some senior politicians have demanded an investigation, saying police could easily have disarmed him.
Rahul Raj, who was in his early 20s, had come to Mumbai recently to look for a job, according to his father, Kundan Pratap Singh.
Mr Singh denied that his son had hijacked the bus, and that there was "something more" to the incident.
News channels showed footage of the man brandishing a revolver and asking for a mobile phone from passengers in the half-empty bus.
At least 15 passengers were travelling in the bus at the time.
Mr Thackeray says jobs should be given to locals
The police said he fired inside the bus, injuring one passenger.
Senior politicians from Bihar state, including the federal railway minister, Laloo Prasad Yadav, expressed shock at the shooting and demanded a judicial probe into the incident.
"The boy did not look like a terrorist. So [the police] could have captured the boy. The police could have spoken to him on the phone and negotiated with him," Mr Yadav said.
Bihar's chief minister Nitish Kumar has said the boy could have been disarmed and arrested.
But Maharashtra's interior minister, RR Patil, defended the police action, saying that no "unstable person can hold hostages with the help of a revolver".
Some reports said that Indian PM Manmohan Singh had expressed concern over the incident and spoken to Maharashtra's chief minister "to ensure" the security of migrant workers in Mumbai.
Raj Thackeray is the leader of the right-wing Maharashtra Navnirman Sena (MNS) party and was granted bail last week after being accused of incitement.
His party has been accused of several attacks on migrant workers in recent months.
Students in Bihar paralysed rail services last week in protest at the ill-treatment they say Biharis have received from the MNS.
The unrest in Maharashtra has forced many migrants to leave their neighbourhoods, but Mr Thackeray has consistently denied inciting it.