The victim had boarded the service to her in-laws' home in the northern state of Punjab when she was abducted Friday and driven to a district bordering the Sikh holy city of Amritsar, local police officer Raj Jeet Singh said.
Five men joined the driver and conductor, who had taken her by motorbike to an unknown address, and took turns to rape the victim before dropping her off near her in-laws' village on Saturday morning, he said.
"Six men have been arrested on allegations of having raped a 29-year-old woman... after forcibly taking her to an unknown location on the night of January 11," the policeman told AFP, adding that a seventh suspect was being hunted.
"The lady, after being kidnapped, was raped brutally throughout the night by the seven accused," he said.
"After raping the victim throughout the night, one of the accused dropped her near her in-laws' house the next morning where she narrated the whole incident to her two sisters-in-law."
He said the extent of her injuries had yet to be established.
The attack is disturbingly similar to the December 16 gang-rape and murder of a 23-year-old student in Delhi, where five men are on trial in a case that has fuelled anger across India over the treatment of women.
Partap Singh Bajwa, a local Congress Party politician, blamed the police for not enforcing stringent checks on buses operating in the state.
"It all happened due to laxity of police as they never bother to check out the buses moving on national highways during night time," Bajwa told AFP.
Protesters across India have called for the police to be more vigilant and sensitive to the growing incidence of sexual assault against women, after details emerged of the New Delhi attack.
Police and prosecutors have outlined how the alleged rapists picked up the student and her male companion in a school bus which they had taken for a joyride after drinking heavily.
The bus would have had to cross numerous police checkpoints at that time of night but at no stage was the vehicle pulled over by officers.
After getting into an argument with the woman's male companion, the group allegedly beat him up and raped the victim in the back of the bus while driving around Delhi for some 45 minutes.
They also sexually assaulted the woman with a rusting metal bar, leaving her with severe intestinal injuries, before hurling her out of the vehicle. She died in a Singapore hospital 13 days after the attack.