By Subir Bhaumik BBC correspondent in Calcutta

Assamese passengers complain to the police (photo: Abhijit Choudhury)

The youths were protesting over alleged discrimination against Biharis who had tried for jobs with Indian Railways in the neighbouring state of Assam.

The attacks happened at five stations where trains bound for Assam had stopped, officials from the state-owned railway network said.

Competition for government jobs often ignites regional rivalries in India.

Police escorts for passengers

Railway officials said some trains bound for the north-east were being diverted from Bihar to stop youths beating more passengers with sticks, rods and belts.

Other trains had been provided with armed police escorts.

Wounded passengers were sent to hospitals in West Bengal state, which lies between Bihar and Assam, according to the railway officials.

The attackers targeted passengers from Assam and other states in India's north-east, and officials said even women and children were beaten up.

At least five passenger trains were attacked, at train stations in the towns of Jamalpul, Munger, Kishanganj and Katiahar.

Letter to president

The violence was triggered by reports that Bihari candidates who had travelled to Assam to take a job test with the north-eastern railway network were forcibly turned away.

However, the All Assam Students' Union says Assamese applicants, not Biharis, have been the real victims of discrimination.

In a letter sent to India's prime minister and president, they said very few locals took the test, and most of the candidates were from Bihar.

The letter also pointed out that the minister in charge of India's railways, Nitish Kumar, was from Bihar.