At least six pilgrims have been killed and 20 others injured in a stampede at a Hindu religious festival in eastern India, officials have said.

The incident occured on Friday during a procession outside the temple of God Jagannath in Orissa state's Puri district, Pramod Mohanty, a senior medical officer, said.

"The dead include three men and three women," Mohanty said, adding that four of those injured in the accident were in a critical condition.

J K Panda, a police inspector, said the stampede occurred as worshippers pressed forward to touch the statue of the goddess Subhadra, which was being carried in a chariot.

About one million people were in Puri on Friday to attend the opening day of the week-long annual chariot festival, authorities said.

Three Hindu deities, Jagannath, Balabhadra and Subhadra, are taken out of the temple and then transported in colourfully-decked chariots to anotther nearby temple for a week's stay.

Pilgrims jostle with each other to pull the chariots, considering it to be a holy task.