Yemen's health ministry estimates that more than 10,000 people seeking life-saving treatment overseas have died from critical health conditions since Sana'a airport was closed, said a group of NGOs including the International Rescue Committee and the Norwegian Refugee Council.
"Denial of access to travel has condemned thousands of Yemenis with survivable illnesses to death", said Mutasim Hamdan, the Norwegian Refugee Council's Country Director in Yemen. "The result is devastating".
"Yemenis awaiting critical medical treatment overseas now have to find alternative routes to leave the country, which include a 10-20 hour drive to other airports, often through areas where active fighting takes place", the statement added.
The closure comes as Yemen is on the brink of starvation, with 20 million people in need of food aid.
The Yemeni Ministry of Health estimated 10,000 people had died because they could not get specialist treatment inside the country, nor could they be flown out to other locations. "The result is devastating; thousands of women, men and children who could have been saved have now lost their lives", said Hamdan.
The Saudi-led coalition that has been bombing Yemen shut down the Sanaa airport a year ago because it was in a territory controlled by its opponents, the Houthi fighters, claiming it needed to be closed due to security concerns.
Fifteen aid groups on Wednesday called on warring parties in Yemen to reopen the country's main airport, saying a year-long closure was hindering aid and preventing thousands of patients from flying overseas for life-saving treatment.
"It is critical that all channels of domestic and worldwide air movement are reopened so Yemenis can get help, and help can get to Yemenis".
Last July, the exiled government of President Abd-Rabbu Mansour Hadi accused the Houthi militias of attacking the Sudanese mission in Sana's.
As well as the deaths of thousands of people, the country's infrastructure has also been devastated.
The protracted war, which has been accompanied by a naval and aerial blockade, has already killed over 12,000 Yemenis.
The relentless bombardment of the impoverished country by Saudi Arabia's warplanes has brought Yemen's healthcare system on the verge of total collapse, destroying hospitals and health facilities, among other civilian targets.
Since March 2015, the Saudi-led coalition of mostly Persian Gulf countries has been carrying out airstrikes against the Houthis at Hadi's request.
According to the ICRC's statement, the highly contagious disease is "a direct effect of a conflict that has devastated civilian infrastructure and brought the whole health system to its knees".