The temple portals were opened by priests for the first batch of pilgrims who started reaching the base camp on the banks of the river Pampa by morning and walked up the steep hill covering a distance of about 5 km to reach the 'Sannidhanam' atop where the temple is located.
The vast majority of pilgrims are men as women between 10 and 50 years are not allowed to visit the shrine as per the traditions followed by the temple.
One of world's largest religious events, the shrine attracts an average of 30 million devotees every year.
Apart from the temple management body Travancore Devaswom Board, various government departments and voluntary agencies like 'Akhila Bharata Ayyappa Seva Sangham' are engaged in efforts to ensure hassle-free inflow of pilgrims both at the 'Sannidhanam' and the base camp Pampa.
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Large contingents of police personnel have been deployed for security, crowd management and traffic control.
The first leg of the pilgrimage will culminate with the 'Mandala' pooja on December 27, which will be followed by 'Makaravilakku' with the 'jyothi darshan' as its finale on January 14.