Humanitarian aid in rebel-held areas usually arrives through Turkey via a cross-border mechanism created in 2014 by a UN Security Council resolution.

But it is contested by Damascus and its ally Moscow, who see it as a violation of Syrian sovereignty.

Under pressure from Russia and China, the number of crossing points has been reduced over time from four to one.

And now areas surrounding that one border crossing have suffered significant infrastructure damage, while the aid workers on the ground have been hit by the catastrophe.

'Lives are at stake'

"Every effort is being done to overcome these logistical hurdles, which are created by the earthquake," Laerke said.

"There is a window of about seven days" when survivors are generally found, Laerke said, adding that it was "critical" to get teams to those in immediate need as soon as possible.

"It is imperative that everybody sees it as a humanitarian crisis where lives are at stake," he said.

"Please don't politicise this. Let's get the aid out to the people who so desperately need it."

He said the UN was intent on using "any and all means to get to people, and that includes the cross-border operation and the cross-line operation from inside Syria".

But Laerke said access by road was "a challenge" and pointed out that the quake had impacted the UN's "own staff, our own contracting partners, our truck drivers that we work with, our national staff".

"They're looking for their families in the rubble... That has had an impact on that operation in the immediate," he acknowledged.

At the same time, he said, partners that deliver aid in northwestern Syria had indicated they were "operational and they are asking for supplies, and they are also asking for funding".

For now though, the specific Syria cross-border humanitarian fund is empty, he warned.