The Pakistani military has deployed troops, tanks and jets in North Waziristan, on the border with Afghanistan, in a long-awaited crackdown on the Taliban and other militants in the tribal area.
Adding to the pressure on the insurgents, two US drone strikes hit compounds in the area early on Wednesday.
Tens of thousands of people have already fled the operation, which the Pakistani military says has killed more than 200 militants, and a fresh exodus is under way.
An AFP reporter in Bannu saw around 3,000 vehicles leaving to retrieve people from Mir Ali, one of towns where the curfew has been eased.
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Registration points and camps have been set up to deal with the influx of people, officials said.
The decision to allow more civilians to leave North Waziristan points to a new, more intense phase of the anti-militant drive, in which ground forces will play a greater role.
"Miranshah and Mir Ali have already been cordoned off. Ground troops will move in after civilians move to safe places," the official said.
"First ground troops will enter in major towns and will then move towards the suburban areas," after strengthening their positions.
"We will then go to the villages and to the mountains," he added, saying the operation would continue until every militant had been eliminated.
A second security official in the northwest confirmed the details. At least five suspected militants were killed in two separate US drone missile strikes in North Waziristan, according to local officials.
Coming just days before the launch of the Pakistani military operation, they also triggered talk of collaboration between the US and Pakistan.