Several other people were treated at the scene on Friday and released. The injured included an American and a Kuwaiti national, police said.
Aljazeera said the blast occurred in the town of Brummana that overlooks the capital and the Mediterranean coastline.
The explosion came as the country was engulfed in its worst political crisis in years.
Residents reported hearing an explosion at about 9.45pm (1845GMT) on Friday, targeting the Rizq Plaza, which has clothing stores on the ground floor and furnished apartments above.
Ambulances attended the scene, and the damage was severe. The explosion started a fire, shattered glass in several nearby buildings, blew out shutters of stores, smashed several cars and knocked down a lamppost.
Firefighters evacuated residents, put out the blaze in the building and doused cars wrecked in the blast.
Rescue workers helped those
injured by the blast
Police and troops sealed off the area. Red Cross workers helped residents who were overcome by smoke and shock amid a sudden downpour.
Rescuers carried a woman on a stretcher and administered oxygen.
One ceiling in the two-storey underground parking lot collapsed on to the vehicles parked there.
Among the injured was a child, an elderly man and a woman, as well as an American journalist identified as David Livingstone who works for the Daily Star newspaper.
An old man, speaking from his hospital bed, said: "We were sitting watching TV when the bomb went off. We were tossed around, shattered glass, doors and bricks on top of us."
Livingstone was watching the news on television at his fiancee's apartment in a building next door.
"There's a sudden explosion. We go flying forward. Lights go out. Complete pandemonium," he said on LBC television from his hospital bed, his head wrapped with a bandage.
Daily Star newspaper
He said four people were slightly hurt: "Nothing, I think, that's serious. But it was scary."
Police said the bomb was placed in the underground parking at the centre, which is on the main stretch of the resort town in pine wooded mountains. A preliminary police estimate put the size of the bomb at about 20kg.
Brummana, about 15km northeast of the Lebanese capital, is lightly populated in winter, but is packed in the summer with Arab and other tourists.
President Emile Lahud's hometown of Baabdat is only a few kilometres up the same mountain ridge.
"We have heard many rumours that an explosion would take place. We thought they were only rumours, but still we were careful," one resident told Aljazeera. "We appointed security guards at our shops. Sales are decreasing, we are losing, more people are falling injured and our homeland is dying."
Lebanon has been in turmoil since the 14 February assassination of former Prime Minister Rafiq al-Hariri in a massive bomb on a Beirut street. Al-Hariri and 19 other people were killed in the blast.
The killing, which the anti-Syrian opposition blames on Syria and its Lebanese allies, triggered massive anti-Syrian demonstrations and an international uproar that forced Damascus to begin withdrawing its army from the neighbouring country after nearly three decades of dominating it.
Police say the bomb was placed
in underground parking
The explosion was the fourth since 19 March, when an explosion ripped through a commercial and residential neighbourhood of New Jdaidah. Four days later, another bomb wrecked a shopping centre in the picturesque port city of Juniah north of Beirut.
Last Saturday, a bomb set fires to factories in an industrial zone in the Beirut suburb of Buchriah.
In all, two people were killed and 24 were injured. All explosions happened late at night, with destruction high but casualties low.
Anti-Syrian leaders have blamed Damascus and allied Lebanese security authorities for the bombings they say are aimed at proving Syrian troops are needed to maintain security in Lebanon.
The pro-Syrian camp blamed saboteurs for destabilising the country in order to invite international intervention.
Pierre Gimayil and Ghassan Mukhaibir, two opposition legislators for the region, blamed security agencies loyal to the government and Syria for the latest bombing.
"It's part of the same chain. They are political messages that aim at breaking up national unity," Gimayil said. "This is a wanton war against the Lebanese people," Moukheiber said.
"This is a wanton war against the Lebanese people"
"I cannot believe that the intelligence people and the general security don't have an idea of who's behind the bombings," Mukhaibir said. "The only way for citizens to respond is not to be frightened."
But Michel Murr, the pro-Syrian deputy parliament speaker who represents the region, also denounced the attack, which he said was preceded by leaflets predicting a bombing. He urged authorities to exert extra efforts to apprehend the culprits.
Sibawaih Hufininyan, a representative at the Lebanese parliament told Aljazeera that opposition and pro-authority sides were blaming each other. "I believe we are all losing."
The bomb explosion came shortly after a major political development in Beirut, when pro-Syrian politicians rejected Prime Minister-designate Umar Karami's decision to step down and instead urged him to form a cabinet.