A number of pilgrims performing hajj in Saudi Arabia have died and many are believed missing, authorities have said.

As of Sunday, local time, 14 Jordanian citizens were confirmed dead by Jordan's foreign ministry, while 17 others were reported missing.

At least six of the victims were said to have suffered sunstroke, ahead of a weather forecast of near 50-degree Celsius heat. The cause of the other deaths was not specified.

The heat had reached 47C in Mecca, and 46C in Mina, according to Saudi meteorological authorities.

Jordan's ambassador, Sufian Qudah, said communication had been established with Saudi authorities to bury the dead or transport bodies requested by their families back home.

He added a search operation was underway to find the missing pilgrims, mentioning the cohort was not a part of the official Jordanian Hajj delegation.

Additionally, five Iranian pilgrims also died, with the Iranian Red Crescent chief Pirhossein Koolivand providing confirmation in a brief statement.

It is unclear whether their deaths were heat-related. 

Harsh summer takes its toll

Hajj is a five-day annual pilgrimage that usually takes place in the holy Islamic city of Mecca around the same time each year. 

This year it is taking place between June 14 and 19, coinciding with the start of Saudi Arabia's harsh summers which can see temperatures rise to highs of about 45C.

A spokesman for the Saudi Health Ministry, Mohammed Al-Abdulaali, told media more than 2,760 pilgrims had suffered from sun exhaustion on Sunday alone.

"Heat stress is the greatest challenge," he said. 

Reporters saw many pilgrims, especially among the elderly, collapsing on the road to the pillars because of the burning heat. 

Security forces and medics were deployed to help, carrying those who fainted on gurneys out of the heat to ambulances or field hospitals. As the temperature spiked by midday, more people required medical help. 

Deaths in the hundreds each year

Stampedes, tent fires, heat and other factors have caused hundreds of deaths at the mass gathering over the past 30 years.

Large crowd numbers, unwelcoming climate, disease outbreaks, and the rites largely being held outdoors, make the pilgrimage all the more gruelling.

Last year saw at least 230 pilgrims succumb to blistering heat and thousands suffer sunstroke.

In 2015, a deadly crush at the hajj near Mecca killed at least 2,070 people.

More than 1.8 million Muslims from across the world are said to be taking part in the event this year, which ends on Wednesday.

ABC/Reuters/AP