Hundreds of thousands of people make a long, tiring trek to the Kashmir mountains each year to look at the natural icy formation, worshipped as a symbol of the god of destruction, Shiva.

But by Monday, just the second day of the two-month-long pilgrimage, devotees only had a tiny stump of ice to look at -- compared to a 3.6-metre (12-foot) high formation that was there a few weeks ago.

"The Shivlingam (Shiv phallus) has melted down completely," Arun Kumar, a senior official of the pilgrimage board, told AFP.

A variety of factors from body heat to global warming were cited as possible causes for its disappearance in the cave located 3,800 metres (12,800 feet) above sea level.

"Hot and humid weather, besides global warming, are responsible for the early melting," said Kumar, without elaborating.

The pilgrimage route to one of Hinduism's top religious sites is heavily guarded by Indian security forces to prevent possible attacks by rebels fighting New Delhi's rule in Kashmir.

Local papers speculated that a glacier above the Amarnath cave was melting -- making the interior warmer -- in line with glacier retreat in the Himalayas linked to global warming.

In previous years the ice form has remained in place until August, but last year the ice shrine failed to form at all -- officials controversially put an artificial one in its place -- while this year it melted two months early.