Prayers take place five times a day, each one lasting for 15 minutes on average. They currently start at around 5 am (0200 GMT) and conclude at around 11 pm. In winter, the day's final prayer is held much earlier.
Last week, President Recep Tayyip Erdoğan announced that the sixth-century building would reopen as a mosque, shortly after a court decision annulled a 1934 decision converting it into a museum.
Erdoğan set the first prayers on June 24, citing preparations to make the domed compound, home to a world-famous mosaic depicting the face of an angel, compatible with Islamic prayers.
Erdoğan also said admission would be free of charge for visitors of all faiths, calling on foreign observers to "respect" the decision.