Russia and China have vetoed a UN Security Council resolution to prolong cross-border humanitarian aid to war-torn Syria, the authorisation for which expires later in the day, diplomats have said.

Thirteen countries voted in favour of the German-Belgian draft, but Russia and China opposed the extension for a second time this week because they favour a more limited proposal.

Russia has proposed a counter-resolution that limits authorisation for humanitarian aid and could now be put to a vote.

Germany and Belgium, two non-permanent Council members that are responsible for the humanitarian aspect of the UN's Syria dossier, yesterday presented the draft that was put to a vote.

"We categorically reject claims that Russia wants to stop humanitarian deliveries to the Syrian population in need," Russian Deputy UN Ambassador Dmitry Polyanskiy wrote in a tweet.

Stopping cross-border aid would be "a devastating blow to the millions of Syrian families who rely on this aid for clean water, food, health care and shelter," warned the NGO Oxfam.

Russia and China on Tuesday vetoed a draft resolution by Germany and Belgium providing for a one-year extension of the cross-border authorisation.

It would have allowed for the maintenance of two crossing points on the Turkish border - at Bab al-Salam, which leads to the Aleppo region, and Bab al-Hawa, which serves the Idlib region.

The UN authorisation allows the body to distribute aid to displaced Syrians without needing permission from Damascus.

Russia and China argue that the UN authorisation violates Syria's sovereignty, and that aid can increasingly be channelled through Syrian authorities.

Syrians protest in Idlib after Russia vetoed the resolution

In January, Moscow, Syria's closest ally, succeeded in having the crossing points reduced from four to two and in limiting the authorisation to six months instead of a year.

Russia, which claims to want continued aid for the insurgent Idlib region, submitted a counter-proposal to the UN Security Council on Wednesday to keep only the Bab al-Hawa access point open, and for six months.

It claims that more than 85% of current aid goes through Bab al-Hawa and that the Bab al-Salam entry point can therefore be closed. But the bid failed when put to vote.

In the only concession to Russia, the new draft asked for just a six-month extension of cross-border aid authorisation, instead of one year. But Germany and Belgium still wanted both border crossings kept open.

According Washington's ambassador to the UN Kelly Craft, keeping only one border crossing open would cut off 1.3 million people living north of Aleppo from humanitarian aid.

One diplomat, who spoke on condition of anonymity, has described the episode as a "showdown" that could drag on.

Another noted that "if the authorisation is renewed a few days late, it is not the absolute end of the world. It suspends the convoys for a few days, it does not put them in danger".

For the UN, keeping as many entry points open as possible is crucial, particularly given the risk of the coronavirus pandemic, which is spreading in the region.

A young girl in Syria is given hand sanitiser by a Goal representative

The first confirmed case of the coronavirus in northwest Syria was in a doctor who worked in the Bab al-Hawa hospital on one of the crossings across the border from Turkey.

The hospital is now locked down and the doctor's close contacts are being traced and put under quarantine.

Derek O'Rourke, Middle Eastern Security Manager with the charity Goal, told RTÉ: "All the measures that we've taken in Europe are simply not possible in camps.

"They're full of displaced people, so they essentially live as refugees, in tents ... with very little sanitation and hygiene.

"We would have to be very worried about the fact that it was a doctor, obviously in contact with vulnerable people. People who are already sick."

He described the local health system in the region as "already shattered" and said the fact that one hospital is already out of action means it will be difficult to treat people if cases there escalate.

Mr O'Rourke added: "Essentially what we will have if the border is closed to humanitarian traffic is that we will have a double whammy - a Covid-19 outbreak and a loss of this capacity to supply humanitarian aid across the border.

"There is no other way to supply humanitarian aid to northwest Syria."

He says that the World Health Organisation is one UN agency that would not be able to gain across the border in the event of a major Covid-19 outbreak in Idlib.

"That would just be a disaster," he said.

In a report in June, UN Secretary-General Antonio Guterres called for a one-year extension of the aid to include the two current access points.

When asked on Thursday if the UN would be satisfied with a single entry point into Syria, body spokesman Stephane Dujarric said: "We need more aid to go through the border. We do not need less to go through."

David Miliband, president of the International Rescue Committee, described the veto as a "dark day" for Syrian civilians and the UN.

He added: "[It] defies logic or humanity to dismantle a system designed to bring life-saving aid to Syrians in the form of food, health supplies, vaccines, and now critical Covid-19 provisions."

Additional reporting Eleanor Burnhill