Iraqi PM Haider al-Abadi has visited Mosul to congratulate Iraqi forces for their “victory” over IS in the city.
Mr Abadi was there to announce the city’s full “liberation”, his office said in a statement.
Iraqi forces, backed by US-led air strikes, have been battling to retake Mosul since 17 October last year.
Islamic State militants seized it in June 2014 before taking much of Iraq’s Sunni Arab heartland and proclaiming a “caliphate” straddling Iraq and Syria.
Kurdish Peshmerga fighters, Sunni Arab tribesmen and Shia militiamen have also been involved in the gruelling battle.
The Iraqi prime minister arrived to “congratulate the armed forces and the Iraqi people” on the final defeat of IS in Mosul on Sunday, the statement said.
He met commanders in the city but has not yet given a speech formally declaring triumph.
Iraqi forces have been battling the remaining pockets of jihadists desperately holding out in a tiny area near the Old City.
Airstrikes and exchanges of gunfire could still be heard on Sunday, and plumes of smoke seen rising into the sky.
Mr Abadi’s spokesman, Saad al-Hadithi, said victory would not be formally declared until the few remaining militants were cleared from Mosul, Reuters news agency reports.
Earlier 30 IS fighters were killed as they attempted to escape the advance of the Iraqi forces by throwing themselves in the River Tigris, state media said.
At the scene – Stench of decaying corpses
Jonathan Beale, BBC defence correspondent
Troops helped a steady stream of fleeing civilians – mostly women and children – to safety. Their faces were haunted and some had to be helped.
The children didn’t even flinch when there was more sound of gunfire. An older woman was so weak she could barely walk. A few babies being carried looked almost lifeless.
The families were given food and water. This was their first taste of freedom after three years of living under IS control. The battle briefly forgotten in their own fight for survival.
If this is victory it’s come at a huge cost. Not just in human life. Nearly everyone rescued had had to leave dead relatives behind.
Almost every building in the old city has been scarred or completely destroyed.
Search and rescue teams are still pulling bodies from the rubble. The heat has contributed to the stench of decaying corpses.
The government announced the “liberation” of eastern Mosul in January, but the west of the city, with its narrow, winding streets, has presented a more difficult challenge.
Some 900,000 people have been displaced from the city since 2014 – about half the the pre-war population – aid organisations say.
As “victory” was proclaimed in Mosul, Save the Children warned of the psychological impact on the children “haunted by memories of extreme violence, or of loved ones killed in front of them”.
“For children and their families to process these horrors and rebuild their lives, psychological support will be absolutely crucial”, said Ana Locsin, Save the Children’s Iraq country director.
“But right now the world is providing next to no funding for mental health.”
IS has lost large parts of the territory it once controlled in Iraq since the regional offensive began.
But the fall of Mosul does not mean the end of IS in the country. It still has territory elsewhere – such as Tal Afar and three towns in the western province of Anbar – and is able to carry out bombings in government-held areas.
French President Emmanuel Macron was among the first to hail the victory of Iraqi forces in Mosul on Sunday, praising the fighters – including French troops in the coalition – who had made it possible.
Britain’s Defence Secretary Michael Fallon also congratulated Mr Abadi.
“Britain has played a leading role in the coalition that has helped bring about the removal of the death cult from Mosul,” Mr Fallon said, referring to IS.
And in a joint statement, EU foreign affairs chief Federica Mogherini and its aid commissioner Christos Stylianides said: “The recovery of Mosul from the hands of (IS) marks a decisive step in the campaign to eliminate terrorist control in parts of Iraq and to free its people.”
They urged called for a “process of return and the re-establishment of trust between communities”.