Reports suggest some of those injured are in serious condition.
It is the latest in a series of at least six recent suicide attacks in Pakistan that have put security authorities on high alert.
City police chief Rauf Khan said the blast at the city's district-court complex killed a judge and several lawyers, as well as relatives of prisoners on trial.
No one has claimed responsibility.
Quetta is the capital of Pakistan's restive Baluchistan Province, which has witnessed several terror attacks in recent months.
Authorities have blamed a number of attacks on Taliban militants fighting security forces in Waziristan's tribal belt, which borders Afghanistan.
(AFP, Reuters, AP)
Afghanistan And Pakistan
Afghan President Hamid Karzai (left) with Pakistani President Pervez Musharraf in Islamabad in October 2005 (epa)
ACROSS A DIFFICULT BORDER. The contested border between Pakistan and Afghanistan is some 2,500 kilometers long and runs through some of the most rugged, inhospitable territory on Earth. Controlling that border and preventing Taliban militants from using Pakistan as a staging ground for attacks in Afghanistan is an essential part of the U.S.-led international coalition's strategy for stabilizing Afghanistan. Officials in Kabul have been pointing their fingers at Pakistan for some time, accusing Islamabad or intelligence services of turning a blind eye to cross-border terrorism targeting the Afghan central government. Many observers remain convinced that much of the former Taliban regime's leadership -- along with leaders of Al-Qaeda -- are operating in the lawless Afghan-Pakistani border region.... (more)