Riyadh (AFP): A bus ferrying pilgrims to the holy city of Mecca burst into flames after a collision on a bridge on Monday, killing 20 people and injuring more than two dozen others, Saudi state media reported.

The incident in the southern province of Asir highlights persistent challenges to safely transporting worshippers to Mecca and Medina, the holiest cities in Islam.

It comes during the first week of Ramadan, a busy time for umrah pilgrimages, and just months before millions of Muslims are expected to make the annual hajj pilgrimage.

"According to preliminary information we have now received, the number of deaths in this accident reached 20, and the total number of injuries was approximately 29," the state-affiliated Al-Ekhbariya channel reported.

It said the victims had "different nationalities" but did not mention them or provide a breakdown.

The channel said the bus had "car trouble", without specifying, while the private newspaper Okaz said the accident resulted from an issue with the brakes.

The vehicle "then collided with a bridge, overturned and caught fire".

Footage broadcast on Al-Ekhbariya showed a reporter standing in front of what appeared to be the burnt-out shell of the bus.

Transporting worshippers around Saudi Arabia's holy sites is a perilous task, particularly during the hajj, when roads can be chaotic with buses creating interminable traffic jams.

In October 2019, some 35 foreigners were killed and four others injured when a bus collided with another heavy vehicle near Medina.