Dozens of Iraqi soldiers celebrated amid the rubble on the banks of the Tigris river without waiting for a formal victory declaration, some dancing to music blaring out from a truck and firing machineguns into the air, a Reuters correspondent said.
The mood was less festive, however, among some of the nearly one million Mosul residents displaced by months of combat, many of whom are living in camps outside the city with little respite from the blazing summer heat.
"If there is no rebuilding and people don't return to their homes and regain their belongings, what is the meaning of liberation?" Mohammed Haji Ahmed, 43, a clothing trader, told Reuters in the Hassan Sham camp to the east of Mosul .
Earlier on Saturday, a military spokesman said the insurgents' defense lines were collapsing, state television reported.
"We are seeing now the last meters (yards) and then final victory will be announced," a presenter said, citing correspondents embedded with security forces fighting in Islamic State's redoubt in the Old City by the Tigris.
"It's a matter of hours," she added.
But Islamic State's Amaq news agency reported "fierce fighting" around the riverside district of Maydan and said its fighters "were holding onto their fortified positions."
"The fighters of Islamic State are collectively pledging (to fight to the) death in Maydan," Amaq said in another online post.
Artillery explosions and gunfire could still be heard during Saturday afternoon and a column of smoke billowed over the Old City riverside, the Reuters correspondent said.
A U.S.-led international coalition is providing air and ground support to the eight-month campaign to wrest back Mosul , by far the largest city seized by Islamic State (IS) in 2014.
Almost exactly three years ago, the ultra-hardline group's leader Abu Bakr al-Baghdadi declared from Mosul a "caliphate" over adjoining parts of Iraq and Syria.