A mobile British clinic has been set up in Mecca to treat British pilgrims amid fears of diseases that spread easily during haj, when the city is packed with people from around 160 countries. More than two million Muslims began the haj in Saudi Arabia this week, some 23,000 of them British. Volunteers at the clinic said that they have already treated over two thousand people since they started arriving in the holy city earlier last week, mostly elderly pilgrims who are more likely to come down with diseases. Saudi Arabia usually hosts some 1.5 million pilgrims from abroad, and grants visas to 500,000 inside the kingdom, but the number often swells to 2.5 million as people sneak in illegally. Huge crowds set the stage for frequent disaster in the haj, which in recent years has been marred by stampedes and hotel collapses. Located outside the Grand Mosque, the clinic is said to be one of the best equipped medical centres at Mecca, with medication for treating burns, viruses and other conditions made available by the Foreign Office, volunteers said. Hundreds of people die of illness or heart attack during haj every year, most of them elderly pilgrims, an official from the Ministry of Pilgrimage Affairs said. Around 500 people died of natural causes during the last haj, but the number of deaths has declined over the years as health services have improved. While overcrowding and spread of disease has always been a worry at haj, this time regional tension between Shi'ites and Sunnis has heightened concerns while authorities remain on the look-out for al Qaeda-linked militant violence -- a fear in recent years.