Witnesses at the site said they saw gunmen firing on worshippers before at least one suicide bomber blew himself up.
|The attack triggered violent |
protests in Quetta
The attack triggered violent protests that compelled Pakistani authorities to impose an indefinite curfew, officials said.
Armed policemen and paramilitary troops were heavily deployed in the city.
The local administration declared the curfew and asked people to remain indoors, officials and witnesses said.
"Curfew has been clamped down in Quetta and paramilitary and police have been deployed to control the rioting," an interior ministry official said.
Asked if the security forces had been given orders to shoot protesters on sight, the official said it was "normal procedure in a curfew situation."
Earlier, protesters gathered outside the hospital where the casualties were taken.
"Angry people are on the streets, they are firing into the air and damaging property," an AFP photographer at the scene said.
Police said the blast occurred in a mosque in the centre of the city, where sectarian violence between the Sunni and Shia Muslim sects have flared up recently.
Mosques usually have more attendees on Friday, Islam's holiest day.
"We were offering prayers when I heard the explosion. I saw bodies blown into pieces," said Khan Ali, a 60-year-old man slightly injured in the blast.
The attack took place between 1.30 and 1.45 pm local time during the main midday prayers.
Last month, 11 police recruits were killed and nine wounded when fighters opened fire on their vehicle in Quetta.
Police described the incident as a sectarian attack, because all the recruits were from the Hazara tribe, which is Shia.
'Unfortunate' says Musharraf
Pakistani President Pervez Musharraf reacted to the blast by vowing strong action against the perpetrators.
However, he said he did not know who was behind the attack.
"I don't know the details of this explosion or who did it," Musharraf told reporters in Paris.
Musharraf said it was “unfortunate” that a small minority was able to derail or undermine national feelings.
Pakistan is a predominantly Sunni state of more than 140 million people.
Hundreds of people have been killed in sectarian violence in Pakistan in recent years.