An initial small explosion was followed by a huge blast just feet from the front of the truck carrying Bhutto during a procession through Karachi. The blast shattered windows in her vehicle and set a police escort vehicle on fire.
Those traveling atop the truck with Bhutto climbed down, with one man jumping off while others used a ladder. Bhutto's lawyer, Sen. Babar Awan, said that the former premier was safe.
CBS News correspondent Sheila MacVicar reports that at least one of the blasts is believed to have been set off by a suicide bomber. She spoke with British journalist Christina Lamb who was riding in the truck with Bhutto.
"Suddenly there was this enormous blast and a huge ball of orange flame came across the top of the bus and we were all thrown to the floor," Lamb said, "and everyone screamed 'down, down!'"
Karachi police chief Azhar Farooqi told Dawn News that Bhutto was rushed from the area under pre-laid contingency plans.
"She was evacuated very safely and is now in Bilawal House," Farooqi told Dawn News television, referring to Bhutto's residence in Karachi.
A senior official from her Pakistan People's Party (PPP) told CBS News that Bhutto "was not in great danger at any time after the blast. Thank god she is safe."
Footage from the scene of the blasts showed bodies on the ground, lying motionless, plus a dozen or more injured who were moving. At least one vehicle was burning.
Bhutto flew home after eight years in exile to lead her Pakistan People's Party in January parliamentary elections, drawing cheers from supporters massed in a sea of the party's red, green and black flags. The police chief said 150,000 were in the streets, while other onlookers estimated twice that.
The throngs reflected Bhutto's enduring political clout, but she has made enemies of Islamic militants by taking a pro-U.S. line and negotiating a possible political alliance with Pakistan's military ruler, President Gen. Pervez Musharraf.
CBS News' Farhan Bokhari reports that Ms. Bhutto's return to Pakistan had been preceded by intelligence reports suggesting that members of Al Qaeda were planning to target her. Upon her arrival on Thursday, she set aside the security plan to be visible only from behind a bullet proof glass and instead chose to stand on an elevated platform, raising objections from Karachi police officials who said, Ms Bhutto had compromised her security.
Authorities had urged her to travel in Karachi by helicopter to reduce the risk of attack. But Bhutto, hated by radical Islamists because she supports the U.S.-led war on terrorism, brushed off the concerns.
"I am not scared. I am thinking of my mission," she had told reporters on the plane. "This is a movement for democracy because we are under threat from extremists and militants."
A senior Pakistani security official in Islamabad said the blasts did appear to be the work of al Qaeda though no one immediately claimed responsibility. "Car bombs of this kind bear the hand prints of al Qaeda", he told CBS News on the condition that he would not be named.
The United States condemned "the violent attack in Pakistan and mourns the loss of innocent life there," said Gordon Johndroe, foreign affairs spokesman for President Bush. "Extremists will not be allowed to stop Pakistanis from selecting their representatives through an open and democratic process."