Muslim worshippers prayed on Mount Arafat during the high point of the hajj pilgrimage as authorities urged them to avoid the hottest hours of the day after tragedy struck last year.

Thousands of white-robed pilgrims recited Koranic verses from dawn on the 70-metre rocky rise near Mecca on Thursday, where the Prophet Mohammed is believed to have given his last sermon.

But numbers thinned by midday following official warnings for pilgrims to stay inside between 10 am and 4 pm.

Saudi authorities have taken steps to reduce the risk from heat at the hajj, which has drawn more than 1.6 million pilgrims to one of the world's hottest regions, according to fresh figures published on Thursday.

Barring a few years of Covid restrictions, this hajj season has recorded the lowest number of pilgrims in over three decades.

The dip comes after 1,301 people died in temperatures that hit 51.8 degrees Celsius last year – most of them illegal pilgrims, according to Saudi authorities, who implemented stringent measures to reduce their numbers this season.

Unregistered, non-fee-paying pilgrims lack access to the full amenities offered during the hajj, including air-conditioned tents, making them particularly vulnerable to heat-related health risks.

On Thursday, ice packs were handed to people walking towards Mount Arafat, with some placing the small bags on their heads.

With temperatures reaching 42 degrees, officials ushered people away if they spent too long in one place near the bouldered hill, which had fans spraying mist and cool air at its foot. (AFP)