The gods and the demons were constantly engaged in wars. But they united to churn the ocean to produce the nectar that would make them immortal. They lifted the great Mandara mountain and used it like a churning rod, utilising serpent Vasuki as the rope. But the earth began to sink under its weight. So Vishnu assumed the form of a giant tortoise and got underneath the Mandara mountain serving as a base on which the mountain could pivot.
The complete saga is pictorially depicted in a traditional Kalamkari work. Vishnu is shown as half tortoise and half-man, the lower half being tortoise. He carries in the upper two hands, the wheel and the conch and the mace in the lower left hand. Besides the gods and the demons, the pictorial canvas also depicts what emerged from churning of the ocean, besides Amrit, the essence of immortality; the celestial nymphs, Lakshmi, the goddess of fortune, the wish cow Surabhi, the Purna-Kalasha, the royal elephant Airavata etc.
This description by Renu Rana.