Heavy rains and flooding killed at least 48 people in Saudi Arabia, as Muslims began their annual pilgrimage, the Hajj.

The day-long downpour flooded streets, causing traffic jams and electricity outages, and prompting people to stay indoors.  Authorities say some 900 people were stranded as many pilgrims tried to make their way from the Saudi Arabian port city of Jeddah to the Muslim holy city of Mecca. 

At least 2.5 million people are expected to take part in the Hajj, and authorities are also working to address concerns about swine flu and safety.

Four pilgrims have died from swine flu since arriving in Saudi Arabia.  The kingdom's health minister says 67 others have been diagnosed with the virus.

Saudi officials began a swine flu vaccination campaign ahead of the Hajj rites.

Saudi authorities have also set up checkpoints along the roads leading into the cities of Mecca and Medina to guard against any possible sabotage by Shi'ite rebels who they say may have infiltrated the country from Yemen.

The Hajj is one of Islam's five obligations - or pillars.  Every Muslim, if able, must perform it at least once during his or her lifetime.

Some information for this report provided by AFP, AP and Reuters.