Iraqi forces have entered a neighbourhood in West Mosul for the first time since launching an operation to retake it from so-called Islamic State (IS) five days ago.
It comes a day after troops retook the city’s airport from IS.
The army’s assault takes them from desert and farmland into a densely packed city, where fighting is expected to be particularly hard.
IS are dug into the west after being driven out of eastern Mosul last month.
Iraqi forces carried out heavy air strikes overnight ahead of the ground attack on the city itself.
Leaflets warning residents of an imminent offensive were earlier dropped over the west of the city.
The UN has voiced concern about the welfare of civilians trapped in western Mosul.
Aram Shakaram, the country deputy director for Save the Children in Iraq, told the BBC he believed relatively few people had been able to escape since Wednesday.
He said the charity believed that nearly 800,000 people were still trapped there.