Hundreds of devotees from various parts of the country witnessed the holy event.
Bishop of Thanjavur Dr M Devadass Ambrose presided over the flag hoisting ceremony.
After special prayers, the holy flag was taken in procession around the church through Velankannibazaar, Ariyanattu Street and Beach road and was hoisted later.
Following the flag hoisting ceremony, holy mass, litany and benediction were conducted.
Police had made tight security arrangements.
During the festival days (August 29-September 8), holy mass will be conducted at the main shrine and high mass in Tamil, Marathi, English, Konkani, Malayalam, Telugu and Hindi will be conducted at the Basilica from morning till evening.