It was the third attack in the holy city in the last two days as Shi'ites observe the anniversary of Imam Mohammed al-Mehdi's birthday, one of the annual pilgrimages that have evolved into shows of strength for Iraq's majority Shi'ites since the fall of Sunni dictator Saddam Hussein in 2003.
The latest blast occurred near a security checkpoint in Kerbala, 80 km (50 miles) southwest of Baghdad, and most of the casualties were police officers, police and provincial council officials said.
On Friday a car bomb exploded in a garage near a hospital west of Kerbala. Police said four people were killed and 20 wounded.
In a separate incident, a bomb placed under a parked car killed two people and wounded four others in northern Kerbala on Friday, according to an army commander, while a hospital source said the blast killed three people and wounded 23 others.
Shi'ite religious rites were banned under Saddam. They have been targeted frequently by Sunni Islamist insurgents since the U.S.-led invasion that deposed him.
Last year car bombs killed and wounded scores of people during the Imam Mehdi observance in Kerbala.
While violence has fallen sharply in Iraq in recent years, militants still launch hundreds of attacks each month.