A state of emergency has been declared in the province, and police and troops are on the streets with all residents ordered to stay in their homes.
Kandahar Provincial Council head Ahmed Wali Karzai told RFE/RL's Radio Free Afghanistan that 800-900 inmates of Sarposa prison are now on the run in the volatile province, which was a traditional Taliban stronghold.
"No one knows the number exactly, but there were around 390 Taliban prisoners in that prison and around 600 or 700 more [who] were criminal prisoners. Two hundred prisoners are still here in the prison -- the rest of them escaped," said Ahmed Wali Karzai, who is Afghan President Hamid Karzai's brother.
He said many of the escaped Taliban were high-ranking field commanders who "were organizing suicide attacks." He ran off a list of names that included Mullah Kayom, Mullah Gulbari, Mullah Kayom, Khaled Agha, and "some others who were extremely important."
"They were important because they were able to do most of the assassinations, the killings of government officials and suicide attacks and these types of activities," he said of the escapees.
A Taliban spokesman, Qari Yusof Ahmadi, confirmed that its fighters were behind the commando-style attack, carried out by at least one suicide bomber and other militants using small arms fire and rocket-propelled grenades.
Afghan Deputy Justice Minister Mohammad Qasim Hashimzai said that NATO-led "ISAF forces [and] government security department officials are now checking the roads around Kandahar" and inspecting vehicles "to see if they can capture inmates [trying] to leave the city."
At least 15 security guards were reported killed in the assault. Hashimzai said that around 10 p.m. "a suicide bomber, together with a truckload of ammunition and explosives," destroyed the prison gate before rockets were fired to demolish the top floor of one of the prison blocks to "open the way for the inmates to manage to escape."
"I was in my shop [when] suddenly I heard a huge bang and I was so afraid -- all the windows of my shop broke," shopkeeper Abdul Sattar said. "Some 20 minutes later, I came out of my shop and saw armed men and prisoners running toward the villages and orchards. When I came back in the morning, I saw that the prisoners had escaped and our shops were destroyed."
Deputy Justice Minister Hashimzai said that, as a precaution, the prison's chief official, Abdul Qabir, is under investigation for possible involvement.
Karzai suggested that the breakout is a major security breach that will be of great concern to the Afghan central government and security forces. "People in Kandahar are used to this type of things, but it's a big blow to the security forces," he said. "It was a huge success for the Taliban."
Kandahar Province is one of the key battlegrounds in the Taliban's insurgency against President Hamid Karzai as well as Afghan and foreign troops.
In May, hundreds of inmates at Kandahar jail ended a weeklong hunger strike after a parliamentary delegation promised to address their demands. They were demanding fair trials and complained of torture by prison authorities.
A group of Taliban prisoners briefly took control of a block in Pol-e Charkhi prison in Kabul in 2006 before it was recaptured by security personnel. Several inmates and security personnel were wounded in the armed encounter.
In 2005, four foreign Al-Qaeda members escaped from a high-security prison at Bagram airfield, Afghanistan's main U.S. military base, north of Kabul.
with additional Reuters reporting