Delhi police launched a formal investigation on Saturday after receiving a direct complaint from the woman. In photo: Indian Christians attend a peace protest in Ahmedabad on March 20, 2015.
The woman said that the tour guide spiked her bottle of water and raped her with four of his acquaintances inside her hotel room.
Police are now verifying the woman's timeline and tracking the suspects, including by checking security camera footage from the hotel, AFP reported.
Last month, a 35-year-old Japanese tourist was raped in southern India. Another Japanese tourist was raped last year in the western city of Jaipur, less than a month after six men gang-raped a 22-year-old Japanese tourist in the eastern city of Kolkata.
Five men were sentenced for life in June this year for or gang-raping a 52-year-old Danish tourist in New Delhi in 2014.