Last year, 1,301 pilgrims, most of them unregistered and lacking access to air-conditioned tents and buses, died as temperatures soared to 51.8 degrees Celsius.

Here are some incidents that have marred the centuries-old pilgrimage:

- Stampedes -

The worst hajj disaster ever took place in 2015, when a stampede during the stoning of the devil ritual in Mina, near Mecca, killed up to 2,300 worshippers.

Some pilgrims blamed the stampede on the closure of a road near the stoning site, accusing security forces of mismanaging the flow of worshippers.

Two weeks before, more than 100 people were killed and hundreds injured when stormy weather toppled a crane onto Mecca's Grand Mosque.

Some 364 pilgrims died in a 2006 stampede, which came a week after a hotel collapse in the city centre killed 76 people.

Two years earlier, 251 people died in a stampede, and in 1998 more than 100 people were killed.

Authorities cited "record numbers" of pilgrims as the cause of a 1994 stampede that killed 270 people.

In 1990, 1,426 mostly Asian pilgrims perished, trampled underfoot and asphyxiated in a tunnel at Mina after a ventilation system failed.

According to the authorities, panic set in inside an already hugely overcrowded tunnel when seven pilgrims fell from a bridge.

Witnesses said a power outage paralysed the tunnel's two powerful ventilators.

- Attacks -

In 1989 a twin attack outside of the Grand Mosque on July 10 killed one person and wounded 16. Weeks later, 16 Kuwaiti Shiites were found guilty and executed.

A decade earlier, hundreds of gunmen calling for the abdication of the Saudi royal family barricaded themselves inside Mecca's Grand Mosque on November 20, 1979, taking dozens of pilgrims hostage.

The official toll of the assault and subsequent fighting, which took place after the hajj was over, was 153 people dead and 560 wounded.

- Protests -

Saudi security forces in 1987 suppressed an unauthorised protest by Iranian pilgrims on July 31 in which more than 400 people including 275 Iranians were killed, according to an official toll.

- Infernos -

A fire on April 15, 1997 caused by a gas stove ripped through a camp housing pilgrims in Mina, killing 343 people and injuring around 1,500.

In 1975, a huge fire on December 14 started by an exploding gas canister in a pilgrim camp close to Mecca killed 200 people.