Iraqi troops are moving into Tikrit on several fronts, pushing back Islamic State (IS) militants to the city centre, officials said.
Forces have retaken areas and key sites in the north, south and west, including a police headquarters and a hospital, reported the BBC.
Iraq's defence minister said that phase two of the operation would begin soon.
Nearly 23,000 soldiers are involved in the offensive to retake Saddam Hussein's hometown.
This is the biggest offensive launched by the Iraqi government since the terror group captured large parts of the country last June.
