TAEZ, Yemen (AFP) — Lorries filled to the brim with goods labour up and down the dangerously winding and precipitous road of Hayjat al-Abed, the mountainous lifeline to Yemen's third largest city.

Unlike all other routes linking southwest Taez to the rest of the war-torn country, the road — with its dizzying drop-offs into the valley below — is the only one that has not fallen into the hands of the Huthi rebels.

Some 500,000 inhabitants of the city, which is besieged by the Iran-backed Huthis, depend on the seven-kilometre stretch of crater-filled road for survival, as the long conflict between the insurgents and the government shows no signs of abating.

Convoys of vehicles big and small move at a snail's pace as they squeeze past each other on the narrow road that has been severely damaged over the years by heavy rainfall.

"As you can see, it is full of potholes, and we face dangerous slopes," Marwan al-Makhtary, a young truck driver, told AFP. "Sometimes trucks can no longer move forward, so they stop and roll back."

Makhtary said nothing was being done to fix the road, and fears are mounting that the inexorable deterioration will ultimately bring the supply of goods to a halt.

Dozens of Taez residents on Tuesday urged the government to take action, forming a human chain along the road — some of them carrying signs saying: "Save Taez's Lifeline".

"We demand the legitimate government and local adminstration accelerate efforts to maintain and fix the road," said one of the protesters, Abdeljaber Numan.

"This is the only road that connects Taez with the outside world, and the blocking of this artery would threaten the city."

'Humanitarian disaster'

Sultan al-Dahbaly, who is responsible for road maintenance in the local adminstration, said the closure of the road would represent a "humanitarian disaster" in a country already in crisis and where the majority of the population is dependent on aid.

"It is considered a lifeline of the city of Taez, and it must be serviced as soon as possible because about five million people (in the province) would be affected," he told AFP.

 Governance in Taez is complicated, with the internationally recognised government practically absent and the city split and under the control of rival groups — some linked to Yemen's Muslim Brotherhood-influenced Al-Islah party and others to Salafists, another Islamist movement.

 Meanwhile, the city's government-appointed governor Nabil Shamsan has little power, and any influence over the province is undermined by internal divisions.

Yemen has been ravaged by the five-year conflict between the Huthis and the government, which is supported by a Saudi-led military coalition. 

The United Nations has called it the world's worst humanitarian crisis with tens of thousands killed since 2015.