Enormous crowds of worshippers headed to Mecca, Islam's holiest city, Friday for the biggest hajj pilgrimage in years, with more than two million expected to brave the scorching Saudi Arabian heat.

This year's hajj -- one of the world's biggest annual religious gatherings -- could break attendance records, officials said.

"As the hajj draws near, the Kingdom of Saudi Arabia prepares... for the largest Islamic gathering in history," Minister of Hajj and Umrah Tawfiq Al-Rabiah said in a video published by the ministry this week.

More than two million people from more than 160 countries will attend, Rabiah said -- a dramatic increase on the 926,000 from last year, when numbers were capped at one million following the COVID-19 pandemic.

About 1.5 million pilgrims from abroad had already arrived by Wednesday evening, Saudi authorities have said.

In 2019, about 2.5 million people took part. Only 10,000 were allowed in 2020, at the height of the coronavirus pandemic, rising to nearly 59,000 a year later.