A US tourist has been gang-raped by a truck driver and two of his accomplices after hitching a ride in the northern Indian state of Himachal Pradesh, police say.

"The 30-year-old was raped by men in a truck on Monday night. They offered her a lift and she accepted it," police Inspector Abhimanyu Kumar said on Tuesday from Manali, a tourist destination in the foothills of the Himalayas.

The incident follows the alleged rape of a 21-year-old Irish charity worker in Kolkata at the weekend and comes as the country attempts to tackle endemic sex crime with tougher anti-rape laws.

Mass protests broke out in the capital and other cities in December and January following the fatal gang-rape of a student on a moving bus in New Delhi, a crime which brought simmering anger among women to the surface.

Kumar said medical tests on the US tourist had confirmed she was raped and police were hunting for the accused men around Manali, which is 500 kilometres from the capital New Delhi.

"The woman cannot remember the number plate of the truck and she could not understand what the accused were talking about. They drove the truck to an isolated spot and raped her for nearly one hour," he said.

Kumar said every truck driver in Manali had been ordered to report to the local police station as part of the investigation.

The woman, who cannot be identified under Indian law, had arrived in Manali on Monday and has agreed to stay in the town, a popular back-packing stop for visitors, to help investigations, police said.

"She will have to identify the accused when they are arrested," said another senior police officer, VK Dhawan.

Officials at the US embassy in New Delhi said they were aware of the incident.

The incident comes a day after police in eastern India arrested a local businessman for allegedly drugging and raping an Irish woman after her birthday party at the weekend.

A survey by a trade body released earlier this year found that the number of foreign women tourists visiting India had dropped by 35 per cent following several assaults that have made global headlines.

A Swiss cyclist was gang-raped in the central state of Madhya Pradesh in March and a South Korean tourist was allegedly drugged and raped in the same state in January by the son of the owner of a hotel where she was staying.

New measures passed by Indian MPs in March this year increased punishments for sex offenders to include the death penalty if a victim dies and a minimum 20-year prison sentence for gang-rape.