Media playback is unsupported on your device Media caption Shahzeb Jillani reports on the funeral and speaks to a member of the Ismalli community

The massacre of Ismaili Shia Muslims in the Pakistani city of Karachi was not only shocking because of its scale - but also because survivors who had been left for dead then had to drive themselves to hospital. The BBC's M Ilyas Khan reports.

About 60 people were on the Ismaili community bus when it was attacked.

Four gunmen, presumed to be members of one of Pakistan's many Sunni militant groups, told them to lower their heads and gunned them down in a style reminiscent of the December massacre at Peshawar's Army Public School.

At least 46 men and women were killed together in cold blood.

And no rescue teams or ambulances turned up.

So, after the gunmen had left, one of the survivors came to life, crawled to the driver's seat, got behind the wheel and drove the macabre contents of the blood-soaked vehicle to the nearest hospital - some 3km (two miles) away.

The attack happened in an area which once formed Karachi's vast rural backyard.

In recent years property developers have acquired land to build housing schemes which are still scattered thinly and only slowly coming up.

'I am angry, I am sad... I am Ismaili, I am Pakistani'

Image copyright Getty Images Image caption Thousands have shared messages of solidarity with Ismaili Shia Muslims in Pakistan

'I am angry, I am sad, I am Ismaili, I am Pakistani'

One of them is al-Azhar Garden, a sprawling gated neighbourhood of Ismaili Muslims built by a community organisation and kept connected to the city centre by the community-run bus service.

Wednesday was just another ordinary morning in al-Azhar Garden. The residents were getting on their bus, preparing to traverse the north-eastern hinterland of Karachi as they normally did to get to their places of work in the centre of the city.

But within minutes the bus had been waylaid by the gunmen.

Image copyright Reuters Image caption Hospital staff had mostly corpses to deal with - several survivors also died of their injuries

"I don't know why the driver would stop to let in strangers; it is a community bus, it never stops for random travellers," one resident of the compound told BBC Urdu's Riaz Sohail.

"Besides, this area is only scantily built and there are desolate patches of scrubland where one can get robbed.

"People on the bus have been robbed on a couple of occasions, but nothing like this ever happened before."

A police detective at the scene, Tariq Jadoon, was picking up some bits and pieces from the broken road and putting them in a plastic bag.

Image copyright AFP

Most were empty cases of 9mm pistol and sub-machine gun rounds, strewn across potholes in the road, near some brown stains apparently caused by blood mixing with soil.

Mr Jadoon had also just picked up a blue cap with the markings of a private security agency.

"Perhaps the attackers were wearing uniforms of the security agency, that's why the driver stopped the bus."

There are no eyewitnesses at the moment to describe the attackers.

The driver and most of the passengers are dead. Those who survived are in a critical condition and have not been speaking to the media.

The police, who did speak to some of the survivors, said there were six attackers riding three motorbikes.

They flagged down the bus just a couple of kilometres from al-Azhar Garden, at a comparatively lonely spot along the University Road link, while heading towards the Karachi-Hyderabad motorway.

A woman passenger who police spoke to said one of the attackers had a clean-shaven face and was wearing trousers and a shirt, Geo TV reported.

She said they first singled out two children and asked them to leave the bus, then started shooting the passengers.

The whereabouts of the children are unknown at the moment.

Some relatives of the victims who went to see them in hospital also came back with bits of the story.

"They told me that four of the gunmen climbed in the bus. They were shouting, put down your heads, put down your heads; then they started shooting…" says Qasim Ali, general secretary of the al-Azhar Garden management committee, who had just been to see a couple of injured relatives in the hospital.

One probable witness, the gatekeeper of a house near where the massacre took place, appears to know more than he is willing to share.

"I saw the bus coming in the distance, and heard the firing. It was scary, so I went in and closed the gate," he told BBC Urdu.

"Then the bus stopped, right over there. The firing stopped. Then I heard people from the village gathering at the scene. I came out, and I saw blood splashed across glass windows, and blood dripping from the doors."

Image copyright Reuters Image caption Funeral prayers were said at the al-Azhar Garden community where the victims had lived

Who are the Ismailis?

Ismaili Shias, in common with other Shia Muslims, revere Ali, son-in-law of the Prophet Muhammad, but they also revere the Imam Ismail who died in 765 AD

They interpret the Koran symbolically and allegorically

Spiritual leader Prince Karim Aga Khan is a philanthropist and business magnate. He gives his name to bodies including a university, a foundation, and the Aga Khan Program for Islamic Architecture at Harvard University and the Massachusetts Institute of Technology

He has encouraged Ismailis settled in the industrialised world to contribute to those communities

Qasim Ali says his relatives told him everybody in the bus was in a bad way. Most people appeared to be dead, but some were moaning.

"Then one of our injured residents who knew how to drive the bus got behind the wheel and drove it to Memon Hospital, about 2-3km from the scene of the attack."

The bus driver himself appears to have been killed and the conductor injured.

According to witnesses quoted by the Express Tribune, the conductor was shot in the head and the gunmen presumed he was dead.

There are conflicting reports about whether he then pulled himself from the floor and took over the wheel, or whether another resident did so.

In any event, the man who drover the bus full of bodies is being called a hero.

"He should be given a national award for bravery," one resident, Ali Asghar, told the Express Tribune.