"More than 20,000 people have left the area, many of them have gone to relatives' homes in Peshawar and other peaceful cities while many others rented houses there," said Mutahir Zeb, the top administrative official of Khyber.
The United Nations said the numbers were being verified, but warned that the figure could be inflated by some people taking advantage of the free food and shelter on offer.
"The provincial disaster management authority has registered 3,200 families and we are verifying this number," Dunya Aslam Khan, spokeswoman for the UN refugee agency, told AFP.
"The estimated numbers of the displaced people are likely to come down by 10 per cent because normally people who are not affected by the disasters also join the displaced families just to enjoy the benefits and compensation," she said.
Pakistan's seven tribal districts on the Afghan border are rife with home-grown insurgency, and are strongholds of Taliban and al-Qaeda operatives.
Although Pakistan has fought Taliban militants across much of the region, it has withstood US pressure to wage battle against the Al-Qaeda-linked Haqqani network, which has leadership bases in North Waziristan.