To see Sanaa's Old City for the first time is like "a vision of a childhood dream world of fantasy castles," a visitor once remarked, but official neglect and unruly construction are threatening to destroy that magic.

Yemen's capital is one of the most ancient cities in the world, and entering its oldest quarter has been described "as perhaps the closest thing to time travel" we can experience.

Ancient "tower blocks," some six storeys high, some nine, look like gingerbread castles. With ground floors of black lava stone, their upper storeys are of baked brick decorated with intricate geometric shapes and horizontal bands in gypsum whitewash.

Each quarter has a mosque, a hammam (Turkish bath) and a garden around which the houses were built.

In the past, water used for ablution in the mosque was then pooled to irrigate the gardens, used for growing vegetables, and waste was recycled to heat water in the hammams or for fertiliser.

That rich heritage is reflected in 103 mosques, some built more than a millennium ago, 14 hammams and more than 6,000 centuries-old houses, and the Old City was declared a UNESCO World Heritage Site in 1986.

But preservationists are struggling against the ravages of the modern world. Randomly built concrete houses distort the Old City's skyline, salt from the cement weakens its structure and the once-spacious gardens are disappearing.

Many people have abandoned their homes, which are costly to maintain, and moved to new villas outside of town. So the Old City has increasingly become a home for lower income people, who are even less able to stem the tide of dilapidation.

More and more of these houses, each of which stands as an individual piece of art, are collapsing because of decay, the recent installation of sewage pipes along the narrow alleys and heavy rainfall.

This is compounded by a lack of maintenance resulting from the indifference of the authorities, UNESCO warns.

And because of inadequate drainage, the rainy season poses an annual threat to the old mud brick buildings.

In February 2012, UNESCO urged the authorities "to ensure the protection of the cultural heritage" of the impoverished country. But the government has been absorbed by an ongoing political crisis and security threats, and had little time, or money, to spare for preservation.

Yemen was rocked by an Arab Spring-inspired uprising in 2011 that forced then president Ali Abdullah Saleh out of office after a year of clashes in Sanaa between loyalists and opponents using medium and heavy weaponry.

Naji Saleh Thawaba, president of the General Organisation for the Preservation of the Historic Cities of Yemen (GOPHCY), said the government is now focused on holding a national dialogue to end political deadlock in the country.

"The government and the international community have only one thing in mind: the national dialogue, and have forgotten everything else -- including heritage," he said.

Founded in 1990, GOPHCY is an independent body that was set up to develop a strategy for sustainable development in Sanaa and other cities.

Thawaba's bitter remark suggests his agency does not have the means to do the job.

"The ministry of finance has not allocated anything to the organisation, which is expected to prepare studies about preservation and prevent abuse," he said.

Thawaba's deputy, Ammatelrazzaq Jehaf, shares his concerns.

"We have a budget of five million riyals ($23,000/17,700 euros) for Sanaa... How can this amount be enough to take care of 600 houses?"

"The only practical solution is a UNESCO mission which would unify national and international efforts to preserve this heritage. Without such a mission, nothing will change," says Thawaba.

Jehaf hopes UNESCO will reach out by "finding donors and financiers who would come to the aid of Sanaa."

UNESCO has organised several missions to Sanaa to try to provide assistance to restoration projects.

But the UN organisation said no official information is available on the state of conservation of Old City properties "due to security restrictions."

Sanaa residents feel their precious heritage is about to crumble, and blame authorities for not doing enough to protect it.

"We have no government attention while many homes are on the verge of collapse," said Abdelaziz al-Dhahiani.

Another resident, Wazir al-Ghallab, echoed the sense of helplessness.

"We cannot restore them ourselves. We keep waiting for government intervention that never arrives. There are houses that have been ruined for 15 years and nobody cares," he said.

"Sometimes the facade is slightly restored but the interior is left in ruins," said Ghallab.

"Old Sanaa is an unmatched jewel that everyone should try to preserve."