Some who fled the jail in the town of Bannu, near unruly ethnic Pashtun tribal areas close to the Afghan border, were militants, an intelligence official said.
One inmate who escaped was on death row for involvement in an attempt to assassinate former Pakistani President Pervez Musharraf, a second police official said.
Pakistan’s al Qaeda-linked Taliban movement, which has close links to al Qaeda, said its fighters mounted the assault, which triggered clashes. Several people were wounded.
“We have freed hundreds of our comrades in Bannu in this attack. Several of our people have reached their destinations, others are on their way,” a Taliban spokesman said.
The claim could not be immediately verified.
If the al Qaeda-linked Taliban freed the prisoners, it could deal a psychological blow to Pakistani security forces following government assertions that security crackdowns have weakened the group.
While the Taliban in neighbouring Afghanistan have staged several jailbreaks, such operations are rare in Pakistan, one of the most unstable countries in the world.
Pakistan is seen as critical to U.S. efforts to stabilize Afghanistan. Yet the South Asian nation faces its own major security challenges.
The Tehrik-e-Taliban Pakistan (TTP), or Taliban Movement of Pakistan, is seen as the biggest threat, staging suicide bombings and shootings in a drive to impose its harsh version of Islam in the nuclear-armed country.
Major suicide bombings have eased in recent months, but it is unclear whether that is due to military gains or a shift in Taliban tactics.
A loose alliance of a dozen groups, the TTP began its battle against the state in 2007, after a bloody army raid on Islamabad’s Red Mosque, which was controlled by its allies.
The assault, ordered by Musharraf, was widely seen as the event which sparked a full-blown Islamist militant challenge to the state.
A police official identified one of the inmates who escaped as a “dangerous prisoner” named Adnan Rasheed who took part in one of the attempts to kill Musharraf.
“He was a mastermind in (one of the attacks) on Musharraf. These people came for him and took another 383 people too,” the official told Reuters, speaking on condition of anonymity.
Police and intelligence officials said only some of the prisoners who escaped were militants.
“Dozens of militants attacked Bannu’s central jail in the early hours of the morning, and over 300 prisoners have escaped,” senior police official Mir Sahib Jan told Reuters.
“There was intense gunfire, and rocket-propelled grenades were also used.”
Paramilitary troops and security forces surrounded Bannu Central Jail. Of a total 944 prisoners in the jail, 384 escaped, said another police official.
Militants apparently targeted six jail blocks in the attack, he said.
The Pakistani Taliban are closely linked with the Afghan Taliban. They move back and forth across the porous border, exchange intelligence, and provide shelter for each other in a region U.S. President Barack Obama has described as “the most dangerous place in the world”.
