Terrified civilians, who stayed put in the Syrian border town of Tal Abyad, sent panicked messages saying they had “nowhere to hide” when the Turkish warplanes first snarled overhead.

Just seconds later, Turkey president Recep Tayyip Erdogan announced his troops, alongside their Syrian rebel allies, had launched an offensive against Kurdish forces in northeast Syria “to prevent the creation of a terror corridor across our southern border, and to bring peace to the area.”

The controversial incursion was effectively green-lighted by President Donald Trump who announced three days ago that US soldiers supporting Kurdish-led forces in the area would step aside and allow it to happen.

“Operation Peace Spring will neutralise terror threats against Turkey and lead to the establishment of a safe zone, facilitating the return of Syrian refugees to their homes,” the Turkish leader added.

But the United Nations has repeatedly warned any military operation would seriously endanger the lives of 1.7 million people based there, particularly as 700,000 of them already rely on aid.

Multiple human rights groups told The Independent that the fighting could spark the displacement of as many as 300,000 people, triggering a “humanitarian catastrophe”.

In Tal Abyad, streams of families fled by road as the first waves of airstrikes struck the outskirts of the city in the afternoon. Similar scenes were playing out in Ras al-Ayn, just 100km to the east.

In pictures: Turkey launches operation in Syria Show all 9 1 /9 In pictures: Turkey launches operation in Syria In pictures: Turkey launches operation in Syria Turkish tanks driving to the Syrian-Turkish border town of Jarabulus yesterday AFP/Getty In pictures: Turkey launches operation in Syria Turkish-backed gather on the outskirts of Jarabulus, Syria, ahead of an offensive on 24 August 2016 Reuters In pictures: Turkey launches operation in Syria Turkish army tanks make their way towards the Syrian border town of Jarabulus, Syria August 24, 2016 Reuters In pictures: Turkey launches operation in Syria Turkish soldiers return from Syria to Turkey with tanks after a military operation at the Syrian border as part of their offensive against the Islamic State (IS) militant group in Syria, Karkamis district of Gaziantep, Turkey, 25 August 2016 EPA In pictures: Turkey launches operation in Syria Turkish army tanks and Turkey-backed Syrian opposition forces move toward the Syrian border as pictured from Karkamis, Turkey, AP In pictures: Turkey launches operation in Syria Turkish tanks on their way to the Turkish-Syria border during an operation against Isis on 24 August 2016 EPA In pictures: Turkey launches operation in Syria Syrian opposition fighters being transported during preparations to enter Jarabulus in Karkamis, Turkey, on 24 August 2016. EPA In pictures: Turkey launches operation in Syria An air strike hitting Isis-controlled territory near Jarabulus, near the Turkish border, on 24 August 2016. EPA In pictures: Turkey launches operation in Syria A Turkish army tank and an armoured vehicle stationed near the border with Syria. Turkish media reports say Turkish artillery has launched new strikes at Isis targets across the border AP

Sara, a Syrian Kurd in Tal Abyad, who asked to remain anonymous, told The Independent the Kurdish population were particularly concerned they would be targeted for their ethnicity by the Turkish forces.

“Residents are extremely scared. The air is full of tension. Children are crying and the parents are helpless,” she said, sounding visibly shaken.

“The town is on high alert. People here are afraid of a possible genocide by the Turkish enemy. It is disastrous.”

A few kilometres south civilians reported families flooding into the neighbouring countryside to escape the fighting.

“People began to leave their homes from around 10am, and fled to the countryside amid a swirl of rumours. Shelling is now everywhere along the border,” said one local journalist, who asked not to be named for fear of backlash.

“They are worried about what the Syrian rebel fighters will do, particularly Kurdish citizens; they remember previous battles.”

Turkey’s rebel allies in northern Syria did little to assuage fears, saying on Wednesday they would show no mercy to Syrian Kurdish fighters in the northeast, whom they said had left them no choice but to battle.

“Strike them with an iron fist, make them taste the hell of your fires,” the National Army, the main Turkey-backed rebel force, told its fighters.

Several rights group told The Independent that last year they had documented multiple “indiscriminate attacks” committed by the Turkish military and its allied armed groups, and to a lesser extent Kurdish forces, in the towns of Afrin and Azaz in northern Aleppo, killing scores of civilians.

All feared a repeat with this incursion.

The UN and the aid agencies estimate that between 100,000 to 300,000 people could flee their homes if the fighting continues. Many of these people have already been displaced multiple times and are already living in terrible conditions.

“One of our immediate concerns is the displacement crisis, all the camps are already massively underfunded,” Sara Kayyali, a Syria researcher for Human Rights Watch, told The Independent.

“There is unlikely to be the capacity to respond,” she added.

Sonia Khush, Syria director for Save the Children, said aid agencies had not yet managed to put down infrastructure like water networks in the pre-existing camps, let alone new ones which may have to be set up.

She feared that the most vulnerable would be foreign children from 40 countries, including the UK, who came out of Isis-held territory last March and are now in specialised camps that may come under Turkish control if the offensive continues long enough.

We have nowhere to hide. We have no bunkers Sara, Kurdish resident of Tal Abyad

“There are more than 9,000 children and we are asking their countries to repatriate them immediately, while they still can,” she said.

“The worst-case scenario is that we lose access to these children, we don’t know if we can get aid to them or how they can be sent home safely.”

Ms Kayyali said that the other concern was the track record of so-called safe zones in Syria, particularly since Turkey made it clear it would “repatriate” Syrian refugees in Turkey to the northern corridor.

“Whenever there is a safe zone, we see more violations inside of it,” she said. “It is impossible to guarantee the safety of these civilians, it is very concerning Turkey would actively force people into these areas.”

Smoke seen rising across Syrian border as Turkey launches offensive

Angelita Caredda, of the Norwegian Refugee Council, urged an immediate halt in the fighting.

“We must see the world’s top powers commit to peaceful negotiations and seek an agreement, which protects civilians in the region,” she said.

“The people of northeast Syria have already endured a humanitarian crisis – is the US or Turkey ready to push them into another one?” she added.

Back in Tal Abyad, Sara said that most of the 10,000 people who live in the city have fled.

“We have nowhere to hide. We have no bunkers,” she said as warplanes circled overhead.