Soon after the explosions, security forces sealed the roads linking Baqouba to Baghdad in an apparent effort to prevent further attacks.
Shortly after midday, another car bomb went off near a fish market in the northern Baghdad suburb of Taji, killing seven shoppers and wounding 25, police said.
Baqouba and the surrounding Diyala province was once the site of some of the fiercest fighting between US forces and insurgents in Iraq, and it remains a hotbed for terrorist attacks.
Iraq is facing a spike in violence, with recent monthly death tolls rising to levels notThe area is religiously mixed, and witnessed some of the worst atrocities as Shiite militias battled Sunni insurgents for control in the years after the 2003 US-led invasion.
The three car bombs used in the attack near Baqouba were deployed in different locations in and around the market in order to inflict most damage and casualties, police officials said. One of the vehicles was a pickup truck loaded with produce that was parked inside the market itself.
Last Friday, Diyala was the site of another deadly bombing.
A suicide attacker drove an explosives-laden car into a bus carrying Iranian Shiite pilgrims visiting holy shrines in Iraq, killing 11 and wounding more than two dozen. The attack took place in the town of Muqdadiyah, about 90 kilometres north of Baghdad.
Provincial councilman Sadiq al-Husseini blamed that attack and today`s bombing in the produce market on al-Qaeda-linked groups.