A storm was responsible for toppling a massive crane that crashed into Mecca's Grand Mosque, Saudi officials say.

Key points: Storm responsible for toppling crane in Mecca

Storm responsible for toppling crane in Mecca At least 107 people killed

At least 107 people killed Images on Twitter show bloodied bodies across courtyard

At least 107 people were killed when the construction crane crashed as worshippers gathered for weekly Friday prayers just days before the annual Muslim Hajj pilgrimage.

"The incident took place as a result of heavy rains and high wind speeds," a spokesman for the Saudi Civil Defence Authority said.

"This led to the uprooting of trees and other minor damage. The collapse of the crane is the result of the high winds, which caused deaths and also injuries."

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.

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 several-storey-high building.

A video on YouTube showed people screaming and rushing around right after a massive crash was heard and as fog engulfed the city.

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.

Local journalist Kamal Idris said that Saudis and foreigners lined up on Friday night to give blood in response to the tragedy.

Outside one hospital, more than 100 people waited in the street for their turn to donate, he said.

The Islamic Heritage Research Foundation said there had been little regard for safety during the massive construction work being done to expand the Grand Mosque.

Irfan al-Alawi, co-founder of the 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.

The Department of Foreign Affairs said it was not aware of any reports of Australians killed or injured in the accident.

Hajj pilgrimage will go ahead: official

Loading

Saudi officials have said this year's Hajj pilgrimage will still go ahead.

Hundreds of thousands of faithful from around the world had already arrived for the Hajj, which is expected to start on September 21.

The Hajj is one of the five pillars of Islam, and every capable Muslim is expected perform it at least once in their life.

"It definitely will not affect the Hajj this season and the affected part will probably be fixed in a few days," said an official who declined to be named.

"Hajj will go on."

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.

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

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

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.

ABC/AFP/Reuters