Media playback is unsupported on your device Media caption The BBC's Orla Guerin says Quetta is regularly targeted

At least 79 people are now said to have been killed in a bomb attack in a predominantly Shia Muslim part of the south-western Pakistani city of Quetta.

The blast, which also wounded 180 others, ripped through a crowded market place in an ethnic Hazara area at around 18:00 (13:00) on Saturday.

A Sunni extremist militant group has said it was behind the bombing.

It is the second major attack on Quetta's 600,000-strong Hazara community in five weeks.

A twin suicide bomb attack at a crowded snooker club on 10 January killed at least 92 people and wounded 121.

Analysis After the last bomb attack in Quetta, and the ensuing protests by the Hazara community, the Pakistan government sacked Baluchistan's chief minister, Nawab Aslam Raisani, but has yet to arrest the culprits behind the attack. This came as no surprise to the Hazara community, who have yet to see the Pakistan government take action against the Sunni extremist group Lashkar-e-Jhangvi. Many Hazaras feel the government is not doing enough and allows groups to act freely against Shia. With frequent targeted killings and bomb explosions in Quetta, the Hazaras are living in a state of fear. Many are apprehensive to leave their homes and those who work in areas that are deemed dangerous are told by their employers to stay at home.

The banned Sunni militant group Lashkar-e-Jhangvi claimed responsibility for the January attacks; and has reportedly claimed responsibility for this latest bombing.

The bomb went off in a market area housing grocery stores, vegetable shops, language schools and a computer centre.

It happened as people, mainly women, were shopping for groceries and children were coming out of their classes.

The district is dominated by ethnic Hazaras, who mostly belong to Pakistan's Shia minority.

Quetta police chief Mir Zubai Mehmood told the media that some 70kg to 80kg explosives had been planted inside a water tank that had been installed on a tractor trailer.

The blast brought down nearby buildings, and police said they feared some people remain trapped under the rubble.

Image copyright AFP Image caption Many women and children are believed to have been victims of the blast

Victims were rushed to hospitals in the area, and some were flown to hospitals in the southern city of Karachi, police said.

"I saw many bodies of women and children," an eyewitness at a hospital told Reuters. "At least a dozen people were burned to death by the blast."

Who are the Hazaras? Image copyright Getty Images Mostly settled in the central Afghan highlands, around Bamiyan province - area known as the Hazarajat

Of Mongolian and Central Asian descent

Legend has it they are descendants of Genghis Khan and his soldiers, who invaded Afghanistan in the 13th Century

Practise Shia Islam, in predominantly Sunni Afghanistan and Pakistan

At least 600,000 live in Quetta, mostly migrants from Afghanistan, who settled there because the city made it easy for them to visit their home communities

Quetta is also on a key Shia pilgrimage route to Iran

Sunni extremists have regularly accused the Hazaras of being proxies of Iran in Pakistan

Angry crowds are reported to have gathered in the area immediately following the blast, pelting police and initially refusing to let them and rescue workers reach the scene of the blast.

The police raised the number of casualties several times through the day.

Quetta is the capital of Balochistan province, which borders Iran and Afghanistan, and has been plagued by a separatist rebellion as well as sectarian violence.

The city's minority Shia community have been angered by what they say is a lack of protection for them against sectarian attacks by Pakistani Sunni militants.

Hundreds of Shia Hazaras in Quetta have been killed in such attacks over the last several years.

Following the attacks on 10 January, families of the victims refused to bury their dead until they received assurances of security from the authorities.

Following talks with Shia representatives from Quetta, Pakistan's Prime Minister Raja Pervez Ashraf sacked Balochistan's chief minister and promised them better security.

In the past Shia leaders and human rights campaigners have accused Pakistan's government of incompetence or collusion, the BBC's Orla Guerin reports from Islamabad.