Saudi authorities on Saturday were investigating a construction crane collapse that killed at least 107 people during a storm at Mecca's Grand Mosque, days before the annual hajj pilgrimage.

Panic broke out as the massive crane came crashing down on the mosque, one of Islam's holiest sites, as the faithful gathered for weekly Friday prayers.

Hundreds of thousands of pilgrims have already arrived in Mecca for the hajj, one of the world's largest religious event which last year drew two million Muslims.

A Saudi official said this year's hajj would go ahead despite the tragedy.

Indonesia, the world's largest Muslim-populated nation, said two of its nationals were killed, while Malaysia and Iran said its citizens were among those injured.

As world leaders offered condolences, the governor of Mecca region, Prince Khaled al-Faisal, ordered an investigation into the incident.

Abdel Aziz Naqoor, who said he works at the mosque, told AFP he saw the massive construction crane fall after being hit by the storm.

"If it weren't for Al-Tawaf bridge the injuries and deaths would have been worse," he said, referring to a covered walkway that surrounds the holy Kaaba, which broke the crane's fall.

The Kaaba is a massive cube-shaped structure at the centre of the mosque towards which Muslims worldwide pray.

Pictures of the incident on Twitter showed bloodied bodies strewn across a courtyard where the top part of the crane, which appeared to have bent or snapped, had crashed into the building which is several storeys high.

A video on YouTube showed people screaming and rushing around right after a massive crash was heard.

The wreckage of the red and white crane was seen lying across the floor of the mosque, while several other cranes towered over the site.

On Fridays, the Muslim weekly day of prayer, the Grand Mosque is usually at its most crowded.

Many faithful would have been gathered there ahead of evening maghrib prayers, which occurred about an hour after the tragedy.

Ahmed bin Mohammad al-Mansoori, spokesman for the two holy mosques, was quoted by the official Saudi Press Agency as saying part of a crane collapsed at 5:10 pm (1410 GMT) "as a result of strong winds and heavy rains".



'Worldwide condolences'

Irfan al-Alawi, co-founder of the Mecca-based Islamic Heritage Research Foundation, compared the carnage to that caused by a bomb.

He suggested authorities were negligent by having a series of cranes overlooking the mosque.

"They do not care about the heritage, and they do not care about health and safety," he told AFP.

Alawi is an outspoken critic of redevelopment at the holy sites, which he says is wiping away tangible links to the Prophet Mohammed.

Indonesian foreign ministry spokesman Arrmanatha Nasir said that in addition to the two Indonesians who lost their lives, more than 30 were injured, some seriously.

"The consular general is still moving from hospital to hospital to find out if there are more Indonesians who are injured and have not yet been reported."

Malaysia said 10 of its nationals were hurt and six unaccounted for.

Tabung Haji's search and rescue team is working with Muaassah Asia to find the missing pilgrims.

Iran's official IRNA news agency, quoting the head of the Hajj Organisation, said 15 Iranian pilgrims were among those injured.

Most of them were treated as outpatients, Saeid Ohadi said.

Condolences came from around the world.

Indian Prime Minister Narendra Modi, whose country is home to tens of millions of Muslims, expressed his sorrow over the incident.

"My thoughts & prayers are with the families of those who lost their lives in the crane crash in Mecca. I wish the injured a quick recovery," he said on Twitter.

Britain's David Cameron tweeted: "My thoughts and prayers are with those who have lost loved ones at #mecca today".

A massive project is under way to expand the area of the mosque by 400,000 square metres (4.3 million square feet), allowing it to accommodate up to 2.2 million people at once.

SPA said that almost 800,000 pilgrims had arrived by Friday for the hajj, which all able-bodied Muslims are expected to perform if they have the means to do so.