Rebels have downed a second military aircraft in as many days.
The explosives-packed cars were detonated at daybreak on Wednesday in a pro-regime neighbourhood of the mainly Christian and Druze town of Jaramana, residents, state media and a rights watchdog reported.
The blasts ripped through a central square near a petrol station, sending residents fleeing in panic.
There was a ball of fire at the end of a narrow lane, and the impact of the explosions brought walls down onto cars, crushing them and scattering debris over the ground.
Pools of blood and severed body parts were on the streets, said an AFP photographer in the town.
The death toll mounted as the day wore on, with the Syrian Observatory for Human Rights giving tallies of 20, then 29, 38 and later 54.
More than 120 people were wounded, and many residents rushed with them to hospital, while others visited the homes of bereaved families.
"What do they want from Jaramana? The town brings together people from all over Syria and welcomes everybody," one resident told AFP.
Jarmana has now been targeted by four such bomb attacks in three months. It is home to predominantly Christians and Druze, an influential minority whose faith is an offshoot of Shiite Islam.
Sectarian divides are a key factor in Syria's armed rebellion, with many in the Sunni Muslim majority frustrated at more than 40 years of Alawite-dominated rule.
The uprising erupted in March 2011 with peaceful democracy protests, inspired by the Arab Spring. It transformed into an armed insurgency when the government began a bloody crackdown on dissent.
The regime of President Bashar al-Assad, himself from the Alawite offshoot of Shiite Islam, insists it is fighting foreign-backed "terrorists".
The failure of international diplomacy has enabled it to press on with its all-out military campaign to crush the rebellion, and the fighting has resulted in more than 40 000 deaths, according to the Observatory.
In the latest violence, an AFP correspondent on the Syria-Turkey border reported that rebel fighters shot down a fighter jet in the embattled northwest.
The warplane came down in a massive explosion, leaving behind a plume of smoke, the journalist said, reporting several kilometres away from where the jet was downed.
The aircraft was hit by a missile and crashed at Daret Ezza, said the Observatory, a Britain-based watchdog that relies on a network of activists and medics on the ground.
Witnesses said the rebels later captured one of the pilots.
"Two pilots used parachutes to jump out of the plane after it was hit," a witness told an AFP reporter one kilometre away in Tourmanin. "One of them was taken prisoner."
The rebels were seen carrying him and taunting Assad in YouTube videos.
"This is your airplane, oh Bashar," a man said in one video as fire and smoke rose from the mass of broken metal. "The [rebel] Free Syrian Army has downed it."
Balance of military power
It came a day after rebels downed an army helicopter for the first time with a newly acquired ground-to-air missile, in what the Observatory said had the potential to change the balance of military power.
The gunship was on a strafing run near the besieged northwestern base of Sheikh Suleiman, the last garrison in government hands between Syria's second city Aleppo and the Turkish border.
Little more than a week ago, the rebels seized tanks, armoured vehicles, artillery, 120-mm mortars and rocket launchers when they took the government forces' sprawling Base 46, about 12 kilometres (eight miles) west of Aleppo.
The rebels, a mix of military defectors and armed civilians, are vastly outgunned but analysts say they are now stretching thin the capabilities of Assad's war machine and its air supremacy by opening multiple fronts.
Risk consultancy group Maplecroft said the regime's growing reliance on its air power highlights the fact that its ability to quell the insurgency is "limited".
"This is in part due to the fact that the Syrian army has primarily been trained and equipped to fight a conventional war against Israel and as such is ill-suited to combating an insurgency," it said. – Sapa-AFP