The sole border crossing used to shuttle life-saving aid from Turkey into conflict-ravaged Syria has been hit by the deadly earthquake that struck the two countries, the UN said Tuesday.

The 7.8-magnitude quake and its aftershocks hit Turkey and Syria on Monday and killed more than 5,000 people.

"The cross-border operation has itself been impacted," Jens Laerke, spokesman for the UN humanitarian agency OCHA, told reporters in Geneva.

"It is a disaster zone," he said, appealing for politics to be put aside to allow desperately-needed aid to get through.

Disaster agencies said several thousand buildings were flattened across an area plagued by war, insurgency, refugee crises and a recent cholera outbreak.

Concerns have been running particularly high for how aid might reach all those in need in Syria, devastated by more than a decade of civil war.

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.

"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 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."