A pilgrim attending the hajj speaks on a cellphone amid heavy rains in Mecca, Saudi Arabia on Wednesday. (Associated Press)

The heaviest rain to hit Islam's annual hajj pilgrimage in years soaked the faithful and flooded the road to Mecca, snarling traffic as millions of Muslims headed for the holy sites. The downpours add an extra hazard on top of intense concerns about the spread of swine flu.

Pilgrims in white robes holding umbrellas, some wearing face masks for fear of the flu, circled the black cube-shaped Kaaba in the Saudi Arabian city of Mecca, the opening rite for the hajj.

But the shrine — Islam's holiest site — and the nearby rain-soaked streets did not see the usual massive, pushing crowds, because many tried to stay inside nearby hotels or were caught in the traffic jams heading into the city.

Mecca and the nearby Red Sea coastal city of Jiddah often see heavy rains during the winter months, and Wednesday's were unusually strong, swamping Jiddah with 70 mm of rain, more than it gets in a year on average, according to weather officials.

They were the heaviest in years to coincide with the four-day hajj. Already jammed traffic was worsened — with a jam of cars as long as 35 kilometres on the partially closed road between Jiddah and Mecca, and some pilgrims and journalists were trapped in Jiddah.

Perennial dangers

The rains could also exacerbate the perennial dangers of the hajj, a pilgrimage all adult Muslims of sane mind, able body and the means to bear the expenses are required to perform once in their lifetime.

The rites are always a logistical nightmare, as a population the size of a city moves between Mecca and holy sites in the nearby desert over the course of four days.

In the past, the rites have been plagued by deadly crushes caused by congestion as the unimaginable crowds perform the rituals. In 2006, all it took was a piece of luggage dropped by one person to trip up others and cause a pile-up that killed more than 360 people.

A slippery, rain-slicked street could be equally deadly — and with the main rites due to begin outside Mecca on Thursday, Saudi authorities urged those arriving at the holy sites to move cautiously and not to rush.

This year has brought the added worry that the massing of more than three million people from around the world could bring a swine flu outbreak. In the past months, the Saudi government has been working with the United States' Centers for Disease Control and Prevention to set up clinics and precautionary measures to stem any outbreak.

Hassan El Bushra, an epidemiologist in the Cairo office of the World Health Organization, said "there is no evidence that this will cause any kind of spread, including the spread of swine flu." It could even be beneficial if it means crowds are smaller, he said.

So far, four pilgrims have died from the H1N1 virus since arriving in Saudi Arabia in recent days, and 67 others have been diagnosed with the virus, Saudi Health Minister Abdullah al-Rabeeah told the Arab news network Al-Jazeera English.