Firefighters were still at the scene of the fire on Monday morning, more than 36 hours after the blaze broke out.

About 150 people were forced to spend a second night in temporary accommodation as firefighters continued to battle against pockets of fires burning within the complex network of business and residential properties.

A substantial part of the core of the heart of the Old Town of Edinburgh has been destroyed

Divisional Officer David Young

They have said it could take days to totally extinguish the fire, which started on Saturday evening.

A spokesman for Lothian and Borders Fire Brigade said firefighters had a watching brief to make sure that the blaze did not flare up again.

Divisional Officer David Young said the fire was one of the worst in the city for many years.

He estimated that the cost of the blaze would run into many millions of pounds - in addition to the huge amount of disruption caused in the area.

"A substantial part of the core of the heart of the Old Town of Edinburgh has been destroyed," he said.

"We really only have the facades, the outside walls standing, and sadly they may have to be removed as well."

The cause of the outbreak has yet to be discovered and it is still too dangerous for investigators to go far into the damaged premises.

Several properties have been burnt out, including the famous Gilded Balloon comedy venue, and there are fears walls of some buildings may collapse.

Monday morning commuters were warned they faced delays as traffic is diverted away from the area, where a number of roads are closed.

Firefighters' efforts have been hindered by the nature of the buildings

Efforts to stop the fire from spreading to other buildings in the area, including the architecturally significant Adam House, appear to have been successful, although the properties are smoke-damaged.

Listed buildings in the area, designated a World Heritage Site by the United Nations, escaped serious damage.

A spokesman for Lothian and Borders Fire Brigade said: "We think that this could have been a lot worse, because these buildings are tightly packed together and many of them are very old.

"The fact that Adam House has been saved from demolition is a testament to the skill of the firefighters involved."

Local councillor Bill Cunningham added: "Such a large fire disaster in the heart of the Old Town has been a major shock for the community but we are relieved there have been no casualties."

An eight-day walkout by firefighters had been due to begin last Wednesday but was called off by the Fire Brigades Union (FBU) general secretary Andy Gilchrist to allow for talks at conciliation service Acas.

Fire chiefs have said that the army, who provide cover during the strikes, would have struggled to deal with the blaze had the firefighters been on strike.

The fire is believed to have started at about 2015 GMT on Saturday above La Belle Angele nightclub, located behind the Gilded Balloon.

It spread rapidly from a shaft, up through the seven-storey building, affecting residential and commercial premises on various street levels of the Old Town.