More than 470 inmates at a prison in southern Afghanistan have escaped through a tunnel hundreds of metres long and dug from outside the jail.Officials in the city of Kandahar said many of those who escaped from Sarposa jail were Taliban insurgents.
The Kandahar provincial governor's office said at least 12 had since been recaptured but gave no further details.
A spokesman for Afghan President Hamid Karzai said the escape was a "disaster" which should never have happened.
The Taliban said it had taken five months to build the 320m (1,050ft) tunnel. It is believed to have been dug from a house rented by the Taliban.
About 100 of those who escaped were Taliban commanders, and most of the others were fighters with the insurgency. The prison holds about 1,200 inmates.
Second jailbreak Afghan prison escapes
- June 2008: More than 900 prisoners escape from Sarposa prison in Kandahar after a suicide bomber blasted open the gates
- July 2010: 19 prisoners escape after a blast at a prison in Farah province
- November 2009: 12 prisoners escape after tunnelling out of a jail from their cells in Farah province
"A tunnel hundreds of metres long was dug from the south of the prison into the prison and 476 political prisoners escaped last night," said prison director General Ghulam Dastageer Mayar.Kandahar's provincial authorities said that a search operation was under way.
One escapee told the BBC it had taken him about 30 minutes to walk the length of the tunnel. The escape took most of the night and vehicles were waiting at the exit point to take prisoners away.
The jailbreak is the second major escape from the prison in three years.
In June 2008 a suicide bomber blew open the Kandahar prison gates and destroyed a nearby checkpoint, freeing about 900 prisoners, many of them suspected insurgents.
After that, millions of pounds were spent upgrading the prison. The 2008 breakout was followed by a major upsurge in violence.
Afghan politician and former MP Daoud Sultanzai told the BBC that the escape exposes "the porousness of our security apparatus".
He said its penetration by the Taliban was "really a serious matter".
Insurgents considered to be the most dangerous are likely to be held at a high-security facility outside the US Bagram air base, north of Kabul, rather than at the Sarposa prison, analysts say.
Nato forces are preparing for the long process of withdrawal from Afghanistan.
The first stage is the transfer of security powers to local forces from July, but Kandahar is not among the first tranche of provinces and cities to be handed over to the Afghans.
Analysts say that it is only to be expected that those regions will once again be the focus of insurgent activity as the Taliban will be planning to seize them back.