Dozens of people were wounded in the attack, which the state-run news agency said targeted the convoy of Brig. Gen. Wissam al-Hassan, the head of the intelligence division of Lebanon's domestic security forces.
Many Lebanese quickly raised the possibility the violence was connected to the civil war in neighboring Syria, which has sent destabilizing ripples through Lebanon for the past 19 months. Al-Hassan led an investigation over the summer that implicated a pro-Syrian Lebanese politician and one of the highest aides to Syrian President Bashar Assad in plots to carry out bombings in Lebanon.
Friday's blast was also a reminder of Lebanon's grim history, when the 1975-1990 civil war made the country notorious for kidnappings, car bombs and political assassinations. Even since the war's end, Lebanon has been a proxy battleground for regional conflict, and the Mediterranean seaside capital has been prey to sudden, surprising and often unexplained violence shattering periods of calm.
"Whenever there is a problem in Syria they want to bring it to us," said Karin Sabaha Gemayel, a secratary at a law firm a block from the bombing site, where the street was transformed into a swath of rubble, twisted metal and charred vehicles.
"But you always hope it will not happen to us. Not again," she said.
The blast ripped through a narrow street at mid-afternoon in Beirut's mainly Christian Achrafieh neighborhood, an area packed with cafes and shops. Doors and windows were shattered for blocks, and several blackened cars appeared to have been catapulted through the air.
Bloodied residents fled their homes while others tried to help the seriously wounded. One little girl, apparently unconscious and bleeding from her head, was carried to an ambulance in the arms of rescue workers, her white sneakers stained with blood.
"I was standing nearby in Sassine Square and I heard a big explosion and I ran straight to it," resident Elie Khalil said. He said he saw at least 15 bloodied people in a nearby parking lot before medics arrived and took them to a hospital.
Al-Hassan's body was so disfigured in the blast that his bodyguards only realized it was him when they recognized his sneakers, a paramedic at the scene told The Associated Press. The paramedic, who saw the body, spoke on condition of anonymity because he was not authorized to speak publicly.
A Lebanese security official said al-Hassan had just returned earlier Friday morning from Paris, where he was visiting family. He was either on his way from or to work in a non-armored car with his driver, who also was among the dead, the official said. He also spoke on condition of anonymity because he was not authorized to give information to the media.
Eight people were killed, including al-Hassan, and 78 wounded, the state-run National News Agency said..
Syrian Information Minister Omran al-Zouebi denounced the bombing, calling it a "terrorist and cowardly" attack.
Syria's top ally in Lebanon, the Shiite Hezbollah movement, also condemned the attack, expressing its "state of great shock over this terrible terrorist crime."
It called on the authorities to catch the perpetrators and on all political forces in Lebanon to work against "every conspirator against the security, the life, the safety and security of the nation."
In Washington, U.S. State Department spokeswoman Victoria Nuland condemned the blast "in strongest terms." She said the U.S. had no information about the perpetrators.
Al-Hassan had headed an investigation into bombing plots that led to the Aug. 9 arrest of former Information Minister Michel Samaha, one of Syria's most loyal allies in Lebanon, who has long acted as an unofficial media adviser to Assad. According to a senior Lebanese police official, Samaha confessed to having personally transported explosives in his car from Syria to Lebanon with the purpose of killing Lebanese personalities at the behest of Syria.
A military court has since indicted Samaha and Syrian Brig. Gen. Ali Mamlouk of plotting to carry out terrorist attacks. Mamlouk, who was appointed recently by Assad to head Syria's National Security Bureau, was indicted in absentia.
Tensions have been soaring in Lebanon over the conflict next door, and clashes have erupted between Assad supporters and backers of the rebellion against his regime.
Syria and Lebanon share a complex web of political and sectarian ties and rivalries, often causing events on one side of the border to echo on the other. Many of Lebanon's Sunnis have backed Syria's mainly Sunni rebels, while Shiites have tended to back Assad.
Lebanon was hit by a wave of bombings and other attacks that began in 2005 with a massive suicide blast that killed former prime minister Rafik Hariri and more than 20 other people in downtown Beirut. In the following years, a string of anti-Syrian figures were assassinated, several in car bombings. Many Lebanese blamed Damascus for the killings, though Syria denied responsibility.
The last serious bombing was in 2008, when a car bomb killed a senior Lebanese anti-terror police official who was investigating dozens of other bombings. Four others were killed and 38 wounded in the blast in the Christian Hazmieh neighborhood.
Since then, Lebanese saw a relative calm in violence. After the uprising against Assad began in March 2011, there have been sporadic gunbattles between pro- and anti-Assad factions, particularly in northern Lebanon.
"I'm very worried about the country after this explosion," Beirut resident Charbel Khadra said Friday. "I'm worried the explosions will return -- and this is just the first one."