The operation to retake Mosul from Daesh began in October with a 100,000 strong coalition consisting of the Iraqi army, peshmerga soldiers and Popular Mobilisation Forces.
The Iraqi army has started to advance on Western Mosul, with reports of shelling against Daesh targets.
The operation against the Daesh stronghold was launched early on Tuesday.
Earlier, the Iraqi army had pushed to within 2 kilometres of the Tigris River in Mosul's southeast.
Their progress has been slowed by counter-attacks from the terror group in the east of the city.
The troops are part of a 100,000-strong coalition that began the fight for Mosul in October.
Shamim Chowdhury reports from Erbil.