Angry mobs in India set fire to several trains and clashed with police on Thursday during rallies against a new short-term military recruitment scheme.

This week the government announced a temporary recruitment plan to induct young adults into the armed forces for four years -- a major break from the past as non-commissioned ranks are seen as lifetime jobs.

The new recruits will miss out on entitlements enjoyed by existing personnel, including government pensions, unless they are retained after the four-year programme.

Police in the eastern state of Bihar fired tear gas to disperse unruly crowds who set four train carriages alight and tried to storm government buildings.

The protests were "initially peaceful but turned violent at a few places", a senior officer in the state capital Patna told AFP. 

Riot police "acted carefully to avoid opening fire at the protesters. There have been no casualties or serious injuries so far," he added. 

Authorities cancelled nearly two dozen passenger train services and deployed additional police to railway stations in an effort to prevent further destruction.

Bihar has some of India's highest unemployment and poverty rates and has earned a reputation as a state left behind by the country's runaway economic growth of the past few decades.

In January crowds of angry job applicants in Bihar set fire to train carriages, blocked railway tracks and burned effigies of Prime Minister Narendra Modi.

They had claimed that entrance exams for the government-run rail sector were being conducted unfairly.

Unemployment has long been a millstone around the Indian economy's neck, with joblessness figures at their worst since the 1970s even before the Covid-19 pandemic wreaked havoc on local commerce.

Modi's government pitched the new military recruitment plan as a pathway to modernise the armed forces with a younger and leaner soldier corps while also creating hundreds of thousands of new jobs.

Retired general Birender Dhanoa told AFP that India's 1.4 million-strong military was "bloated" and in need of reform, but questioned whether the scheme was the appropriate remedy. 

"Four years is a little on the shorter side and feels exploitative," he said. "We have to examine whether it works well for the armed forces too."

Several other cities across India saw protests over the scheme on Thursday, with police near the capital New Delhi also using tear gas on crowds.