The exodus of hundreds of thousands of people from Mosul in Iraq is "one of the largest and swiftest mass movements of people in the world in recent memory" and will require a rapid humanitarian response from the international community, a leading charity warned.
As citizens fleeing the insurgent-controlled city jammed the road to Iraqi Kurdistan, Save the Children said that those who were still in Mosul and those seeking sanctuary elsewhere faced a growing crisis.
"Massive traffic jams and blocked roads are seriously hindering access and movement of aid, as hundreds of thousands flee from the raging violence and chaos," said Save the Children's acting country director in Iraq, Aram Shakaram.
"As an immediate emergency priority, we will distribute water, food and hygiene kits to people fleeing Mosul in coordination with local authorities and organisations responding to the crisis."
Shakaram said the NGO was extremely worried about how the Kurdistan region of Iraq - which is already home to more than 225,000 Syrian refugees - would cope with the huge influx of internally displaced people.
"As terrified families and children flee violence in Mosul, we are witnessing one of the largest and swiftest mass movements of people in the world in recent memory," he said.
"Reaching out to them is an immediate priority and we appeal to the international community to step up its funding to this growing crisis."
Since state security forces abandoned their positions in Mosul two days ago, leaving Iraq's second city to militants from the Islamic State of Iraq and the Levant, thousands of its residents have headed for the relative safety of the Kurdistan region.
By Wednesday morning, Kurdish security forces were taking no chances at a new checkpoint on the road just outside Irbil, capital of the Kurdistan region. Several dozen uniformed and plain-clothes asayish (security) officers scrutinised everyone who arrived at the checkpoint.
Just inside the parking areas, where several dozen people including pregnant women and children were queuing in the scorching heat, an old Kurdish man in his turban and baggy suit hugged a man in Arabic robes.
"He is a friend from the old days, we did military service together in the 1970s and have been friends ever since," said the Kurdish man, who had come to greet his friend and his family and offer support. The Arab man laughed, adding: "We have come to Irbil for a picnic."
Others were crouched in the scant shade cast by several cabins where paperwork was processed. The Kurdish officers, some of whom said they had not slept for two days, were on edge. One plain-clothes officer said Kurdish officers at the checkpoint had seized a large number of guns from civilians heading to Kurdistan regional government-controlled areas.
According to Shirzad, a taxi driver who has a relative in Mosul and has been ferrying Iraqi army deserters from the checkpoint towards Kirkuk, the price of guns has dropped dramatically since fleeing soldiers began selling theirs.
Abu Abdullah, who left Mosul with nothing but what he was wearing, was one of many waiting to go through the checkpoint. "We don't know what is going to happen, our future is uncertain, we won't go back unless the security services return to their posts," he said.
The Kurdistan regional government is planning to work with the UN to set up a camp for the displaced people.
Dan McNorton, a spokesman for the UN refugee agency, UNHCR, said it was too early to know exactly how many people had fled Mosul.
"We are considering this as an emergency and seeing a huge displacement of people. We're currently looking at what emergency relief is needed in terms of food, tents, and other assistance," he said.
Saleh Dabbakeh, a spokesman for the International Committee of the Red Cross in Baghdad, said that although teams had already distributed cooking equipment to hundreds of Mosul residents, the humanitarian situation was far from clear.
Depending on who you listened to, he said, between half a million and a million people had left Mosul. "It's simply too early to understand the magnitude of the operation, but our people are seeing thousands of cars heading from Mosul to Iraqi Kurdistan. … Yesterday it all came down so fast it surprised everyone."
Dabbakeh also warned of the emergency facing those unwilling or unable to leave Mosul. "There is also a problem with electricity there - and once there is a problem with electricity, it means you have a problem with water supplies. Hospitals so far have been able to deal with the situation, but there have been a large number of wounded civilians and non-civilians. It's a confusing and confused situation."
Timeline of Iraqi jihadists' warpath since US withdrawal from country
Two-and-a-half years after the US withdrawal from Iraq, jihadists now control swathes of the country's northwest along the border with Syria, where they are also fighting.
Below are the main developments in the jihadists' advance, which has been facilitated by the internal conflict between the Sunni minority and the ruling Shiites:
2011: On December 22, four days after the US withdrawal from Iraq, a series of attacks in Baghdad, in which 60 are killed, is claimed by a branch of al Qaeda, the Islamic State of Iraq (ISI). Led by the shadowy Abu Bakr al-Baghdadi, ISI was set up after the US-led invasion in 2003. The ISI is particularly influential in the provinces of Anbar, Nineveh and Kirkuk, where a jihadist insurrection inflicted heavy losses on US forces between 2003 and 2006, especially in Fallujah in Anbar province.
2012: Considering itself mistreated and sidelined from positions of power, Iraq's Sunni minority launches massive demonstrations, which continue throughout last year, especially in Anbar.
Fuelled by Sunni ire and the conflict in Syria, unrest reaches its worst point in five years, with 9,475 civilians killed in 2013 according to the non-governmental organisation Iraq Body Count.
On a daily basis, bombs devastate markets, mosques and even funerals. The jihadists attack prisons and army barracks.
Security forces try to react by breaking up Sunni camps and carrying out huge operations against the jihadists.
2013: Allied to some Sunni tribes and benefiting from the sprawling desert in the west to hide out, jihadists claiming allegiance to the Islamic State of Iraq and the Levant (ISIL), an offshoot of the ISI and which also operates in Syria, emerge in April.
2014: On January 2-4, jihadists take control of Fallujah and parts of Ramadi, and Baghdad faces losing control of major towns for the first time since the US invasion in 2003. Up to 500,000 people may have fled the fighting, according to the United Nations.
On May 5, insurgents attack Samarra, 110km to the north of Baghdad, a symbolic city since an attack against a revered Shiite shrine in 2006 sparked the sectarian war of 2006-2007. After fierce fighting, the army, helped by tribal members, retakes the city.
A month later jihadists attack the university of Anbar in Ramadi and targets in Mosul, the country's second biggest city. On Tuesday, ISIL and other jihadists seize Mosul and take control of Nineveh province, sparking a mass exodus. They also overrun sections of the nearby provinces of Kirkuk and Salaheddin.
The authorities seem powerless faced with the jihadists' dazzling advance. Prime Minister Nouri al-Maliki offers to arm civilians to take on the insurgents.