An estimated 170,000 of the 900,000 civilians forced from their homes in a massive wave of displacement in northwestern Syria are living out in the open, the UN said Thursday.

The largest displacement since the civil war in Syria broke out nearly nine years ago comes in the thick of winter, with temperatures often dipping below zero Celsius and snow covering some districts.

"Harsh winter conditions further aggravate the suffering of these vulnerable people who fled their homes to escape the violence, most of whom have been displaced multiple times over nine years of conflict," the United Nations said.

The largest displacement since the civil war in Syria broke out nearly nine years ago comes in the thick of winter, with temperatures often dipping below zero Celsius
The largest displacement since the civil war in Syria broke out nearly nine years ago comes in the thick of winter, with temperatures often dipping below zero Celsius AFP / Aaref WATAD

In its latest update, the UN Office for the Coordination of Humanitarian Affairs said around a fifth of those newly displaced were sleeping rough.

"Almost 170,000 of those newly displaced people are estimated to be living in the open or in unfinished buildings," it said.

The UN said that the camps sheltering some of the rest were overstretched and that many families were pitching tents on plots with no access to basic services such as latrines.

The Syrian government's offensive has boxed the estimated three million civilians living in rebel territory into an ever-shrinking enclave
The Syrian government's offensive has boxed the estimated three million civilians living in rebel territory into an ever-shrinking enclave AFP / Aaref WATAD

The UN's top humanitarian coordinator Mark Lowcock had warned earlier this week that a ceasefire was needed to avert a humanitarian disaster on a scale yet unseen in the Syria war.

But in a Wednesday vote at the UN Security Council, Russia unsurprisingly blocked a resolution demanding a ceasefire in northwestern Syria.

Backed by Russian warplanes, Syrian government and allied forces have been closing in on the last bastion of armed opposition.

A pincer movement of forces thrusting their way into Idlib from the south and from Aleppo province to the east is boxing holdout rebels into an ever-shrinking enclave.

It is also forcing the estimated three million people into an increasingly confined and densely populated area near the border with Turkey.

The UN has called on Turkey to take in more refugees, arguing that the emergency is extreme.

Turkey, which already hosts the world's largest number of Syrian refugees with around 3.6 million people, wants to avoid another mass influx.

Russia