The ancient temple, believed to be over 1,000 years old, is open to devotees only on the full moon day of the Chitra month every year and witnessed a heavy influx of pilgrims from both states, officials said.

The Idukki district administration said the festival was organised jointly by the governments of Kerala and Tamil Nadu. "Temple doors were opened around 5.30 am, and ceremonial proceedings began thereafter.

Kerala-style rituals were held at the sanctum housing the Mangala Devi deity and at adjacent shrines dedicated to Ganapathi and Siva-Parvathi, while Tamil Nadu-style rituals were conducted at the second sanctum nearby," officials said.