Three people died in Thursday's daylight attack on the Dhanbad-Patna Inter City Express in the eastern state of Bihar.
The dead were two passengers and a security guard dead and at least two passengers were injured, The Times of India reported.
The train had passed through a small station about 1 p.m. when it came to an abrupt halt in a remote forested area near Jamui about 100 miles southeast of the state capital Patna.
"We heard cracking sounds and thought children were throwing stones at the train, not rare on this stretch [of track]," a Times reporter who had been on the train said.
"But soon it became clear these were gunshots. I saw a group of armed boys and girls, in their teens or below 25 years of age, with their heads covered as they carried firearms."
Some passengers began shouting for people to keep down and away from windows while others pulled curtains across the windows, he said.
The attackers sprayed several coaches with bullets and security guards on board returned fire in the clash that lasted for 1 1/2 hours.
"They [the attackers] lobbed crude bombs to break open the doors," the reporter said.
"In the adjoining coach, a bullet passed through the wooden support near the door, hitting a youth who died. The Maoists, however, couldn't gain entry.
"They entered the sleeper coach behind us and asked the passengers to get down. Hiding below my seat, I slightly lifted the curtain and saw them being led to the nearby forest where they were made to stand in a row. The belongings of the sleeper coach passengers were looted," he said.
A railway official said the attackers appeared to be after weapons escaped with several rifles and some ammunition from the train.
Maoists -- also called Naxalites after the village of Naxalbari in West Bengal state where they were formed in the late 1960s -- favor attacking trains and vehicle convoys when they pass through isolated areas.
Naxalites demand more of the wealth from natural resource exploitation -- especially by large mining companies -- be distributed among the poor rural people.
The majority of Naxalites are members of the Communist Party of India - Maoist, banned by the government as a terrorist organization.
More than 1,900 people -- including 570 civilians and 700 security personnel -- have been killed in Chhattisgarh, one of the states worst-affected by Maoist attacks in recent years.
Last month, the government sent 2,000 extra paramilitary reinforcements into Chhattisgarh in the wake of a Maoist attack on a vehicle convoy of Congress Party politicians that killed 27 people and injured 32.
Police estimated between 100-150 Maoists ambushed the group's vehicles along a heavily forested road late in the afternoon as the politicians were returning from a political rally, The Indian Express newspaper reported at the time.
The insurgents felled trees across the road and triggered a land mine before starting a gun battle, police sources said. The group's security officers returned fire but ran out of ammunition.
One survivor said nearly 20 vehicles in the convoy came under attack and insurgents methodically checked most vehicles after the fighting ended.