The massive blasts late on Thursday outside Dagestan's main city, which authorities said may have been triggered by suicide bombers, sent huge yellow flames into the night sky, reduced cars to burned wreckage and left a crater in the ground, television pictures showed.
Investigators said 12 people died, while the emergencies ministry put the death toll at 13.
The latest attacks come just days before President Dmitry Medvedev cedes the Kremlin to strongman leader Vladimir Putin who once famously pledged to "wipe out (militants) in the outhouse."
Investigators said the first blast went off on the outskirts of the city of Makhachkala when a car laden with explosives was detonated near a traffic police post at 10:10 pm (1810 GMT) damaging nearby buildings and cars but causing no fatalities.
The second car bomb went off 15 minutes later hitting policemen, rescue workers and passers-by who gathered had at the scene, investigators said.
Regional police said in a statement that the first blast went off when a suicide bomber parked and detonated his Mitshubishi vehicle near from the traffic police post.
A representative of the Dagestani regional investigators, speaking to AFP, refused to confirm the report but said investigators believed that a suicide bomber caused the second blast when he drove a vehicle into the crowd.
State television said it appeared that the initial blast was aimed at attracting emergency workers and security forces to the scene who were then hit by a more powerful second explosion.
"As a result of the second blast, 12 people died including seven policemen, three employees of the region emergencies ministry's rescue service and two local residents," the Moscow-based investigators said in a statement, adding that more than 100 were injured.
A spokeswoman for the regional emergencies ministry told AFP that the blasts killed 13 people, while another one was considered missing.
Another 122 people were injured, and 83 were hospitalised, the emergencies ministry said.
The twin attacks appeared to bear the hallmarks of bombings conducted by radical militants fighting the Kremlin in the Caucasus where they seek to establish an Islamist state.
The blasts were by far the deadliest attacks in the Caucasus this year and deal a huge blow to Kremlin hopes of restoring relative stability to a region that has been a headache for Moscow since the collapse of the USSR.
The Kremlin has repeatedly vowed to root out insurgents but attacks on officials have become a near-daily occurrence in the Caucasus over the past few years.
"Dmitry Medvedev tasked the head of Dagestan, Magomedsalam Magomedov, with rendering all necessary assistance to families of those killed and wounded as a result of the terrorist acts in Makhachkala," the Kremlin said in a statement.
Putin once said "I sometimes feel sorry" for the militants because of the lack of opportunities available to them in the impoverished Caucasus.
The Kremlin fought two wars against separatist rebels in Chechnya in the 1990s but the insurgency has now become more Islamist in tone and has spread to neighbouring regions such as Ingushetia and Dagestan.