In Baghdad, the Prime Minister, Nouri al-Maliki, has asked Parliament to declare a state of emergency and called on the international community to support Iraq in its fight against "terrorism".
But in the capital, where the population is mostly Shia, there is growing panic and fear that Isis forces may take the Sunni city of Tikrit and then move on to Baghdad.
One woman in Baghdad said: "People are buying up food and may not come to work tomorrow because they think the situation is going to get worse."
She added that her relatives in Mosul who had been living in the western part of the city have moved to the eastern side that is defended by resolute Kurdish Peshmerga troops. She said: "People in Mosul have seen government forces run away so they think the Government will use aircraft to bomb Mosul indiscriminately."
Isis has grown swiftly in strength over the past three years under the leadership of Abu Bakr al-Baghdadi, known as Abu Dua, who took over in 2010 after its previous commanders were killed.
Its propaganda films often show non-Sunni Muslims being executed and its reputation for savagery may have helped demoralise the Iraqi security forces in Mosul.
- Independent