The militant group has controlled the Iraqi city for two years. The battle is expected to be the largest in Iraq since the 2003 U.S.-led invasion that toppled dictator Saddam Hussein, according to Reuters news agency.
Hundreds of thousands of people have fled Mosul in the past few years, but around 1.5 million still live in the city.
Coalition forces anticipate that the offensive will take several weeks, though it’s going quicker than planned, Prime Minister Haider al-Abadi said Thursday.
The below images give a real sense of what those fighting on the ground are dealing with every day: