Turkey is expecting up to one million Syrian refugees to arrive at its frontier as a Russian-backed government offensive in the city of Aleppo intensifies the country's refugee crisis.

Currently some 50,000 people are gathered at the border with Turkey seeking refuge from the conflict as Ankara faces increasing EU pressure to allow them to enter.

It comes as startling new figures reveal the number of migrants to enter Europe by sea so far this year is ten times more than the same period last year - prompting NATO to consider launching a humanitarian naval mission in the Mediterranean.

Shelter: A temporary refugee camp for displaced Syrians in northern Syria, near Bab al-Salameh border crossing with Turkey, taken on February 9, as Turkey announced it is expecting up to one million Syrian refugees to arrive at its border

Refuge: Syrians who have fled the attacks of Syrian and Russian air forces to live in tents and open areas at the Bab al-Salameh border crossing on Turkish-Syrian border near Azaz town of Aleppo

Turkish Prime Minister Ahmet Davutoglu today urged the world to speak out against Russia for 'mercilessly bombing civilian targets' in Syria.

Predicting Russia would eventually retreat from Syria in a similar manner to the Soviet forces who once pulled out of Afghanistan - he warned the country would one day 'pay'.

He said those 'who turned Syria into a bloodbath will certainly pay for it', reiterating claims that Russia's support of Bashar al-Assad had triggered the exodus to the Turkish border.

Turkish Foreign Minister Mevlut Cavusoglu said as many as 50,000 people had reached the border, trying to escape intense Russian bombings around Aleppo. He estimated Tuesday that up to a million more could flee if the onslaught continues.

The International Organisation for Migration today revealed 76,000 migrants and refugees arrived in Europe by sea through the first six weeks of 2016.

This marked a drastic increase from the first six weeks of 2015, when just 11,000 undertook the voyage.

The vast majority of these have arrived in Greece as opposed to Italy, which are respectively known as the eastern and western Mediterranean routes.

A young boy peers through a fence at the Bab al-Salameh border crossing with Turkey

Its estimated some 50,000 people have now amassed on the border, prompting fears of another humanitarian crisis

Children who fled the bombing warm themselves by a fire at one of several border crossings with Turkey

Two children who fled Aleppo try to stave off cold winter temperatures while taking staying at the Bab al-Salameh border crossing

In recent weeks the number of people to amass at the border has reached an 50,000 estimated people

A young child peers out the window of a family car, which many refugees have been using as shelter

An injured Syrian man kisses a child near Oncupinar crossing gate in Kilis, Turkey

A woman plays were her children in a wheelchair at the border gate crossing in southern Turkey

Turkey has so far kepts its border closed to the refugees, although those injured have been allowed to cross

Many of those not injured and unable to cross have been living in makeshift camps scattered along the border

Two elderly women carry food and water back to loved ones at the refugee camp by the Oncupinar border gate

The makeshift camp in Kilis, where these refugees are staying, is built on an old farm

Sheima, 5, lost both eyes when she was hit by a stray bullet in Syria. Here she is on her hospital bed in a small clinic in Kilis

Medics at the refugee camp assist an injured man. The crisis at the border has intensified as Syrian government troops have almost encircled the rebel-held parts of Aleppo

A Syrian doctor tends to an injured man's leg while he stays at the makeshift hospital on the Turkish border

It has prompted calls for NATO to launch a humanitarian naval mission in the area, which head secretary general Jens Stoltenberg said would be considered 'very seriously'.

Stoltenberg said he had spoken by telephone with the German and Turkish defense ministers, and that the issue will be on the agenda at a NATO defense ministers' meeting Wednesday.

He added that 'we are all concerned' and NATO's 28 member countries 'see the need to manage and to tackle the human tragedy,' and the problems associated with it.

Yesterday German chancellor Angela Merkel said she was 'not just appalled but horrified' by the suffering caused by Russian bombing in Syria.

She said she and Turkish Prime Minister Ahmet Davutoglu agreed tomorrow's NATO meeting should discuss how the alliance 'can be helpful with the surveillance situation' in the Mediterranean and assist the Turkish coast guard and the European Union's border agency.

Meanwhile, camps for the displaced along Syria's border with Turkey are at full capacity, aid workers say, as tens of thousands flee a major government offensive in Aleppo province.

In and around the border town of Azaz, families are sleeping in the streets, or up to 20 people to a tent, having left their homes with nothing but the clothes they were wearing.

This elderly man is one of 50,000 thought to have amassed at the border with Turkey in a desperate bid to flee the carnage which has erupted in Aleppo

A man wraps himself in a blanket while trying to fend off the cold after fleeing the airstrikes in Aleppo

Syrians rest in a camp built by a humanitarian organisation near Bab al-Salam border gate in Turkey

Humanitarian organisations are warned the influx of refugees has been so rapid families are running out of places to sleep

An elderly man who has been living in a vehicle on the border gestures to a photographer

A woman airs out blankets and sheets on the side of an abandoned truck on the border with Turkey

Turkish authorities have said 600,000 people could yet amass on the border in a worst case scenario

As well as using abandoned vehicles, some families are crowding up to 20 people into tents at a time

A group of Syrians who fled the attacks in Aleppo sit together at the desolate refugee camp

The refugees come predominantly from the suburbs of Hayan, Haritan, Kafr, Anadan, Kafr Naya, Mayir and Ihris - locations targeted by the Russian and Syrian airstrikes

Syrian families left homeless by the bombing campaign sift through a bag of old shoes and boots

The UN says up to 31,000 people have fled Aleppo and surrounding areas in recent days, as government forces press an offensive that could encircle the rebel-held part of the city.

'There are no longer enough places for families to sleep,' said Ahmad al-Mohammad, a field worker with Doctors Without Borders who enters Aleppo province from Turkey daily.

'Many of them in the first days were sleeping in the streets and outdoors without blankets or covers.'

He said up to 20 people were crowding into tents being distributed by aid groups and which are usually meant for seven only, with homes in towns receiving displaced people also filled to capacity.

He said aid groups were also distributing warm clothes and mattresses, with Turkey allowing humanitarian goods across the border, which remains closed to the fleeing Syrians.

'They are trapped,' Mohammad said in a late Monday telephone interview. 'They've left their homes and everything they have behind, and they can't get into Turkey.'

A young boy peers out the window of his family's car, which sits on the Bab al-Salameh border crossing

A young boy peers at the photographer while sitting in the back of a truck filled with his family's possessions

A group of children among the 50,000 to have fled Aleppo in recent days wash up inside their makeshift shelter

Thousands of Syrians have fled the city of Aleppo following a brutal government offensive on rebel held suburbs

Turkish authorities fear as many as 600,000 people will gather at the border to flee Syria's civil war

A family sit beside old trucks and oil drums as they hope for entry to Turkey

The UN's humanitarian aid agency OCHA said on Monday that eight informal camps on the Syrian side of the border were at 'full capacity.'

And the UN's aid chief Stephen O'Brien said he was 'gravely concerned' by the mass displacement, noting that about 80 percent of the tens of thousands of people on the move were believed to be women and children.

He said: 'We have reports that civilians have been killed and injured, and that civilian infrastructure, including at least two hospitals, has been hit. People urgently require shelter, food and basic household items.'

Syrian government forces backed by allied militias and Russian air strikes began a major operation in northern Aleppo province last week.

They have advanced around much of Aleppo city, virtually encircling the rebel-held eastern part, and prompting tens of thousands to flee their homes in the northern countryside.

They are now around 20 kilometres (12 miles) from the Turkish border.

While Ankara says its open-door policy to Syrian refugees remains unchanged, it has kept the main Aleppo border crossing closed in recent days, focusing on sending assistance to camps just inside Syrian territory.

Many of those living at the camp have nothing more than a blanket for shelter. Others sleep in abandoned cars

A elderly refugee sits next to a row of tents - many of which are overcrowded and overflowing

Thousands of those living at the camp are children. Here youngsters are pictured collecting fresh water

Aid agencies have said the camp sites are already overcrowded while numbers are expected to dramatically increase in the coming weeks putting further strain on resources

A youngster pushes a man on a wheelchair through the makeshift campsite at the Bab al-Salameh crossing

The number of migrants to have crossed into Europe by sea this year is ten times that of the same period last year, new figures reveal

The vast majority of these migrants have entered from Turkey to Greece, via what's known as the eastern Mediterranean route

A man gives the thumbs up to cameras after reaching the Greek island of Lesbos from Turkey today