The celebrations are on in the entire Braj area comprising Mathura, Agra and Hathras districts.
The Yamuna is flowing to the brim. Mathura's ghats are filled with pilgrims who began arriving from Thursday taking advantage of the extended holidays including Independence Day Friday.
An official said an estimated 200,000 people had already gathered in the region.
In Gokul, across the Yamuna, celebrations started Saturday and will continue for three days.
Officials in Mathura said more than 4,000 security personnel have been deployed to secure the Sri Krishna Janmabhoomi campus.
Janmashtami is celebrated by some Sunday and by others Monday.
Faced with a steep demand for flowers, some like the ancient Keshav Dev temple have made arrangements to get fresh supplies from Kolkatta and Bangalore.
Mathura, located about 50 km from Agra and 145 from Delhi, is the birthplace of Lord Krishna.