Iraqi forces say they have taken several villages to the south of Mosul hours after launching a major offensive to retake the western half of the city from Islamic State (IS) militants.
Leaflets warning residents of an imminent offensive were dropped over the west of the city as the United Nations warned hundreds of thousands of civilians could be trapped there.
Iraqi government forces seized several villages as they move towards an assault on the last area of IS-held Mosul.
Hundreds of military vehicles, backed by air power, rolled across the desert towards IS positions on Sunday.
The progress in the south of the city takes them within striking distance of Mosul airport.
Iraqi Prime Minister Haider al-Abadi formally announced the offensive early Sunday.
Army Staff Lieutenant General Abdulamir Yarallah said in a statement that elite Rapid Response units captured the villages of Athbah and Al-Lazzagah - two villages south of Mosul airport.
Government forces retook the eastern side of the city, the last major IS stronghold in Iraq, last month. The western side, with its narrow, winding streets, may prove a bigger challenge.
For now, there is no advance from eastern Mosul as all bridges from there across the Tigris river to the west of the city have been destroyed.
Special forces units safely detonated IS car bombs as they cleared villages south of Mosul, according to the BBC's Quentin Sommerville, who is embedded with the troops.
As well as primed car bombs, the jihadists left behind SIM cards, clothes, instant coffee and weapons as they retreated.
The number of civilians trapped there could number up to 650,000. Charity Save the Children said on Sunday it believed as many as 350,000 of them were children.
Leaflets warning residents of an imminent offensive were earlier dropped over the west of the city.
"This is the grim choice for children in western Mosul right now: bombs, crossfire and hunger if they stay; or execution and snipers if they try to run," said the charity's Iraq country director, Maurizio Crivallero.
The offensive on the eastern part of the city was launched on 17 October, more than two years after jihadists overran Mosul before seizing control of much of northern and western Iraq.
Experts warn that western Mosul, although slightly smaller than the east, is more densely populated and includes districts that are seen as pro-IS.
The UN said in late January that almost half of all the casualties in Mosul were civilians. At least 1,096 have been killed and 694 injured across Nineveh province since the start of October.