Midnight masses and special prayers were held in various churches, including the ancient Santhome Basilica here, as scores of faithful thronged them.
Many a home was decorated with the Christmas tree as young and old relished the Christmas cake even as people across different faiths exchanged greetings.
A Nagapattinam report said thousands of pilgrims from several parts of the country and abroad thronged the Shrine Basillica of Our Lady of Health at nearby Vailankanni, a famous pilgrim centre.
As the clock struck 12 midnight, priests of the Church came in a procession to announce the birth of Jesus. Children carried candles and the Holy Bible in procession.
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Political leaders led by Governor K Rosaiah extended Christmas greetings.
The Governor wished that the holy occasion of Christmas rekindled the spirit of love and compassion and promoted unity and brotherhood.
"Let us live up to the ideals of Lord Jesus Christ and join hands to build a harmonious society," he said.
Chief Minister J Jayalalithaa said Lord Jesus preached equality and one should always follow it.
DMK President M Karunanidhi also extended his greetings, saying Lord Jesus preached love and patience.