More Bangladeshis than Indians are expected to use the service
The passenger train service between Calcutta in India and the capital of Bangladesh, Dhaka, has resumed after an interval of more than 40 years.
Trains travelled in both directions on Monday - the first service since the 1965 war between India and Pakistan.
Bangladesh - previously East Pakistan - gained independence from Pakistan in 1971 but Delhi and Dhaka only agreed to resume the train link in 2001.
The train has been dubbed the Maitreyi, or Friendship, Express.
One service left Dhaka on Bengali New Year's Day on Monday for the inaugural 500km (310 mile) run to Calcutta, with another train running from Calcutta to Dhaka.
The BBC's Bangladesh correspondent - travelling to Calcutta - says some in India have expressed concern that the train could lead to an increase in smuggling and illegal immigration.
Our correspondent says that even though security checks at the border will take four hours, the new train is another sign that normal relations are being established.
Meanwhile the 360-seater Calcutta-Dhaka Friendship Express on its inaugural run was carrying barely 65 passengers, including journalists and politicians, says BBC's Subir Bhaumik who is travelling to Dhaka on the train.
"The inaugural service has been started in a hurry and people are still not aware of where to get tickets. But once they know, the trains will go full and I have no doubt about that," said Indian railway spokesman Samir Goswami.
Bangladesh and India's West Bengal state used to form united Bengal and many people on both sides of the border share a common language and have relatives on the other side.
With one-way tickets starting from $8 (£4), it is expected to be popular with Bangladeshis visiting family, looking for work, shopping or seeking medical treatment in their wealthier neighbour.
One man on the train said he was returning to his village in Bangladesh after 60 years.
"I came to India as a refugee when I was six year old but for me Kalindi in Bangladesh, the village I was born, remains my motherland," said Janatosh Pal, his voice choked with emotion.
DHAKA-CALCUTTA RAIL ROUTE
The route was suspended in 1965 after war broke out between India and Pakistan. Bangladesh was then part of Pakistan.
The first train carrying government officials ran on 8 July 2007.
A one-way ticket costs about £4
Public enthusiasm was palpable and thousands lined up on both sides of the railway track all the way from Calcutta to Gede on the border, waving at the train.
A group representing Hindu refugees from Bangladesh, Nikhil Banga Nagarik Sangha (All Bengal Citizens Committee), briefly obstruct the train because they are opposed to it.
"There is no reason why India should develop close links with Bangladesh when Hindus are persecuted in that country," said the group's chief Subhas Chakrabarti.
Police blamed the group for planting three bombs on the route on Sunday. The bombs were defused and scores of the group's supporters were arrested while demonstrating near the tracks.
Bilateral relations were dogged by suspicion and rivalry for many years even though India helped Bangladesh win its independence from Pakistan, says our correspondent.
Disagreements over security arrangements delayed the implementation of the rail link after the two countries signed an agreement in 2001.
A passenger coach and freight trains already run between the two countries.