Hundreds of sick and elderly Yemenis "will die within the next week" unless Saudi Arabia lifts its blockade and allows urgently needed medical supplies into the country.

Doctors in the capital told Al Jazeera pharmacies across Sanaa that were already struggling with a critical shortage of specialist drugs, would be unable to treat cancer, diabetes and renal failure patients by the start of next week.

"We're running dangerously low on medical supplies and won't have anywhere near the necessary vials of pain-relief medication, insulin, and other specialist medicines for our patients," said Abdulrahman al-Ansi, a doctor at Sanaa's al-Mutawkil hospital.

Ali, a two-year-old boy with acute lymphocytic leukaemia died last month as a direct result of the absence of cancer medications, he said.

"Unless Saudi Arabia eases its restrictions and allows food and medical supplies, I could end up losing all of my cancer patients - even those suffering from diabetes - [a treatable disease] will die. Hundreds will perish in the next week alone."

Saudi Arabia, which has been at war with Yemen since 2015, tightened its air, land and sea blockade of the country on Sunday, after Houthi rebels fired a ballistic missile towards the Saudi capital, Riyadh.

The Houthis, a group of fighters that controls the capital and large expanses of the country, justified the missile attack, blaming Saudi-led air strikes - which have killed thousands of people - of ravaging large parts of north Yemen.

The kingdom has defended the blockade, which bars aid groups like Doctors without Borders, Oxfam and UN agencies from delivering aid, claiming it is aimed at preventing weapons being smuggled into Yemen by its regional rival, Iran.

Tehran has rejected allegations of arming the Houthis, calling them "malicious, irresponsible, destructive and provocative".

The Saudis have taken a page from [Syrian President Bashar] al-Assad's playbook. They think this siege will break us and we'll accept their plan for the country. I may not live to see the end of this war, but I pray the Saudis lose. Mohamed Aboubakr, 62-year-old chemotherapy patient

'Fatal consequences'

Aid organisations in Yemen said they were "greatly alarmed" by Saudi Arabia's decision, warning it could "bring millions of people closer to starvation and death".

"The current stock of vaccines in the country will only last one month. If it is not replenished, outbreaks of communicable diseases, such as polio and measles, are to be expected with fatal consequences, particularly for children under five years of age and those already suffering from malnutrition," said Oxfam, Save the Children, the Norwegian Refugee Council and 19 other aid groups in a joint statement.

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The 22 humanitarian groups also warned Yemen had only six weeks of food aid remaining for about seven million Yemenis who are facing "famine-like conditions".

"The humanitarian situation in Yemen is extremely fragile and any disruption in the pipeline of critical supplies such as food, fuel and medicines has the potential to bring millions of people closer to starvation and death," they added.

Since the start of Sunday's siege, the country's already inflated food and fuel prices have skyrocketed, while flights delivering much-needed humanitarian aid have been prevented from landing.

'Assad's playbook'

"I haven't received my salary in months," Mohamed Aboubakr, a 62-year-old civil servant, who was undergoing chemotherapy at the hospital, told Al Jazeera.

"How am I going to pay my medical bills?" he asked. "Prices have soared since the start of the siege - what am I supposed to do?"

Aboubakr said he had borrowed more than $2,000 from friends and family to pay for the treatment, but with the tightening of the siege, suggested it could have all been in vain.

"The Saudis have taken a page from [Syrian President Bashar] al-Assad's playbook. They think this siege will break us and we'll accept their plan for the country. I may not live to see the end of this war, but I pray the Saudis lose."

The streets of Sanaa were almost free of cars on Thursday due to a fuel shortage, with locals saying public transport fares have doubled.

Azzubair Abdullah Hasan, a medic at a cholera centre in Sanaa's Aljiraf neighbourhood, said even wealthy Yemenis were beginning to feel the pinch.

"Everything has gone up in price," Hasan told Al Jazeera.

"Cooking gas has spiked and filling up my car with petrol now costs YR10,000 ($38) [it cost YR6,000 before the start of the siege], how can people continue with their lives. The situation is unbearable."

Saudi Arabia entered the conflict in Yemen in 2015 after the Houthi rebels took over the capital, Sanaa, and forced Yemeni President Abd-Rabbu Mansour Hadi to flee.

Together with a coalition of other Arab states, and with logistical support from the United States and other western powers, Saudi Arabia has pushed the Houthis from the southern port city of Aden, but has failed to dislodge them from Sanaa and their northern strongholds.

According to the UN, the conflict has killed more than 10,000 people and left over seven million in need of food assistance.

Millions of others do not have adequate access to health, water and sanitation services.

The country has also been hit by a cholera outbreak, with some 900,000 suspected cases since April.