Families have made their way to the self-ruled northern Kurdish region in Irbil to escape the fighting.
Suspected Islamist militants drove Iraq’s security forces from their posts and seized the provincial government headquarters, security bases, and other key buildings in Mosul.
ISIS now controls vast swaths of territory in eastern Syria and western and central Iraq, as it moves to establish a militant enclave on both sides of the border.
The Iraqi prime minister, Nouri al-Maliki, asked parliament to declare a state of emergency on Tuesday, raising further doubts over the army’s ability to control the insurgency following the withdrawal of U.S. troops.
The U.S. called for a stronger response from Iraq to the latest violence, asking Maliki to “step up to the plate.” The sudden collapse of the army has alarmed many in Washington, where Obama has been attacked for failing to do more to ensure security.
Video released by the Iraqi military shows soldiers taking on the militants, but local residents say black flags belonging to ISIS are flying in the center of Mosul.
Paul Hamilos is the world features editor for BuzzFeed News and is based in London.