A fire swept across a pilgrims' encampment outside Mecca Tuesday as 2 million Muslims gathered for one of Islam's most sacred rituals. Witnesses said as many as 50 worshipers died.

The witnesses said the dead were mostly Indians, Pakistanis and Bangladeshis. Ambulances, their sirens blaring, weaved through heavy traffic to rush scores of injured to hospitals, the witnesses added.The fire broke out on the plains of Mina as Muslims gathered for the hajj, or pilgrimage, were beginning to move to the arid plains of Mount Arafat.

There, they will stand together in prayer at dawn Wednesday. The gathering on Mount Arafat, where the Prophet Mohammed delivered his last sermon in the 7th century, is the climax of the hajj.

The hajj recently has been the scene of several tragedies, including the deaths of 1,400 people in a 1990 stampede.

Witnesses said Tuesday that helicopters were brought in to aid firefighters on the ground trying to contain the blaze at Mina, which was spread by high winds and 104-degree temperatures. The fire was contained after several hours.

A second fire was reported in Iranian encampments on Mount Arafat, but it was not known if there were casualties. The official Iranian news agency said fire-fighters were battling that blaze.

Egypt's Middle East News Agency said witnesses reported hearing explosions of gas cylinders, which are used by the pilgrims for cooking, and suggested this could have been the cause of the fire.

The tents, some of them held up by wood framing, were pitched close together and were of a flammable material, the witnesses said.

Cleanup operations were quickly launched, with workers sweeping away the charred remains of hundreds of air conditioners, mattresses and burned pages of the Koran.

Encampments for the hajj are set up by nationality.