The measure came into effect at 0930 IST after security forces launched a major operation against the Kurdistan Workers' Party (PKK) rebels late yesterday, the state-run Anatolia news agency said.
The militants had erected barricades and dug trenches, it said.
A total of 17 PKK militants have so far been "rendered ineffective" in the ongoing operation backed by tanks and helicopters, Anatolia added.
The rebels were still attacking security forces with long-range rifles, it said.
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The Turkish government launched a major campaign against the PKK in late July, aimed at forcing it out of strongholds in southeastern Turkey and northern Iraq.
The group has hit back hard, killing dozens of police and soldiers in almost daily bomb and shooting attacks.
More than 150 soldiers and police have been killed in attacks since July blamed on the PKK.
The government, for its part, claims to have killed more than a thousand rebels - figures that have been treated with scepticism in the independent media.
The Turkish government said that up to 32 PKK rebels were killed during the Cizre curfew.
The renewed violence shattered a two-year ceasefire which had stoked hopes of an end to the PKK's three-decade insurgency, in which more than 40,000 people have died.
Meanwhile in Istanbul, police detained 44 people, including district officials of the pro-Kurdish Peoples Democratic Party (HDP), which the government accuses of being a front for the PKK -- a charge denied by the party's leadership.
The escalation comes ahead of snap general election on November 1.