At least six people have been killed after a car bomb targeting a police patrol exploded on a busy commercial street in the Iraqi city of Tikrit, police say.

Seventeen other people were wounded in Thursday's blast, they say.

They said four policemen and two civilians were killed by the explosion, and police officers were among the wounded.

"An explosion rocked the area and I found myself in the hospital. I have shrapnel in my head," Ashref Abbas, a wounded policeman, said at a local hospital.

The blast damaged about 30 shops in central Tikrit and pools of blood were seen in the street.

Police swarmed the area, firing shots in the air.

Tikrit, which is located about 150km north of the Iraqi capital, Baghdad, is the capital of Salahuddin province and hometown of Saddam Hussein, Iraq's former president.

Overall violence has dropped sharply in Iraq since the worst days of the sectarian conflict in 2006-07 but bombings and shootings are still regular, often targeting police and government workers.
   
Hundreds of people have been killed since an inconclusive March 7 parliamentary election that has yet to produce a new government.