UNITED NATIONS -- UN Secretary-General Antonio Guterres on Thursday announced that the world body will launch a flash appeal for donor support for those affected by the earthquake in Syria next week.

"The earthquake that struck Turkiye and Syria is one of the biggest natural disasters in our times," Guterres told reporters, warning that "we haven't yet seen the full extent of the damage and of the humanitarian crisis unfolding before our eyes."

He pointed out that the earthquake struck as the humanitarian crisis in northwest Syria was already worsening, with needs at their highest level since the conflict began.

Guterres said that the first UN convoy, which included six trucks carrying shelter and other desperately needed relief supplies, crossed into northern Syria Thursday through the Bab al-Hawa crossing on the border with Turkiye.

"More help is on the way, but much more, much more is needed," he said, adding that the United Nations has done its best to race to respond and are committed to doing much more.

The UN's Central Emergency Response Fund has released 25 million U.S. dollars to jumpstart the response.

"By early next week, we will launch a flash appeal for donor support for those affected by the earthquake in Syria," Guterres said, adding that the United Nations is also ready to support the Turkish government's response "in any way we can."

Guterres said he has asked UN Undersecretary-General for Humanitarian Affairs and Emergency Relief Coordinator Martin Griffiths to travel to areas affected by the earthquake this weekend.

Griffiths, already in Turkiye, will also visit Aleppo and Damascus in Syria to assess needs and see how the United Nations can step up support.

In addition to more resources, Guterres stressed the need "to explore all possible avenues to get aid and personnel into all affected areas."

"This is the moment of unity, not to politicize or to divide, but it is obvious that we need massive support," he told reporters. "I would be very happy if in relation to the UN, there will be the possibility to do it also in as many crossings as possible."

"This is a moment in which everybody must make very clear that no sanctions of any kind interfere with relief to the population of Syria in the present moment," he said.

Devastating earthquakes struck Turkiye and Syria on Monday, leaving nearly 20,000 people dead in the two countries so far, according to latest data.