Benazir Bhutto, the former Pakistani prime minister, has been killed in a gun and suicide bomb attack at an election rally in the city of Rawalpindi.
At least 16 others were also killed in Thursday's attack with another report saying at least 20 bodies were seen after the explosion which triggered violent protests across the country.
Bhutto,54, was proclaimed dead after she was taken to the Rawalpindi General Hospital. "
At 6:16pm [13:16 GMT], she expired," Wasif Ali Khan, a member of Bhutto's Pakistan People's Party (PPP), present at the hospital, said.
Police said a suicide bomber fired at Bhutto as she was leaving the rally venue in a park before blowing himself up.
"The man first fired at Bhutto's vehicle. She ducked and then he blew himself up," Mohammad Shahid, a police officer said.
Pervez Musharraf, the Pakistani president, reportedly chaired an emergency cabinet meeting after the blast.
Bhutto's supporters vented their anger
after her killing [AFP]
He later appealed to the nation to remain calm "so that the evil designs of terrorists can be defeated," state TV reported.
But as news of Bhutto's death spread, supporters at the hospital in Rawalpindi smashed glass doors and threw stones at cars.
Angry supporters also took to the streets in the northwestern city of Peshawar as well other areas, and raised anti-Musharraf slogans.
Thousands also gathered on the streets of Karachi, the capital of Bhutto's native Sindh province.
In Rawalpindi, at the site of the attack, Bhutto's supporters burned election posters from the ruling party and attacked police, who fled from the scene.
The interior ministry respondend by putting its forces on red alert.
Following the blast, body parts and flesh were strewn across Liaqat Bagh park where Bhutto had spoken.
Police cordoned off the street with white and red tape, and rescue workers rushed to carry victims in to ambulances.
Nawaz Sharif, also a former Pakistani prime minister, told grief-stricken Bhutto supporters outside the hospital: "I assure you that I will fight your war from now on."
He said he shared the grief of "the entire nation".
Javaid Manzoor, the president of Bhutto's PPP party, told Al Jazeera: "We are shocked. We are stunned. Every single one of us is mouring the loss of our leader."
Al Jazeera's Sohail Rahman said questions would now be raised about security there.
The killing is likely to deepen the political crisis in Pakistan, where radicals had vowed to disrupt the vote and Musharraf's opponents, including Bhutto, accused him of planning to rig the result.
Manzoor said he believed the poll, sheduled for January 8, would now be cancelled.
Bhutto had served twice as Pakistani prime minister between 1988 and 1996.
She had returned to Pakistan from an eight-year exile on October 18.
Her homecoming parade in Karachi was also targeted by a suicide attacker, killing more than 140 people.
On that occasion she narrowly escaped injury.
Earlier on Thursday, four people were shot dead and three wounded at an election rally of Sharif in Rawalpindi.
Sharif blamed supporters of the party that backs Musharraf.
The attacks are the worst directly related to the January 8 polls since campaigning intensified in mid-December.