Nineteen prisoners, most facing terrorism charges, escaped from a temporary prison in Iraq's northern city of Kirkuk through a ventilation window, a senior local police official has said.

Police patrols had been deployed on Friday around the city, which sits 250km north of Baghdad, and a search was on for the escapees, police sources said.

"Nineteen detainees escaped. They removed the ventilator in the bathroom and used blankets to jump from the opening," Major-General Torhan Abdulrahman, the city's deputy police chief, told the Reuters news agency.

"Most of them are accused in accordance with article 4 [terrorism]. Investigations are ongoing," he added. 

Police sources said the incident occurred before sunrise at the main temporary prison in central Kirkuk, which is housed inside a fortified police compound.

Prisoners are usually held there while waiting to be tried in court. Youssef said it was the first time such an incident had occurred in the city.

Mosul escape

Last September, 35 prisoners facing terrorism charges escaped via a sewage pipe from a temporary jail in the northern
city of Mosul, an al-Qaeda stronghold which has seen a number of big prison breaks. Iraqi police were able to recapture 21 escapees.

Kirkuk, where the population is a volatile mix of Arabs, Kurds, Turkmen and others, is at the heart of a long dispute between Iraq's central government and the autonomous Kurdish region, which lays claim to the city and its rich oil reserves.

Violence has dropped dramatically in Iraq since the height of sectarian warfare in 2006 and 2007, but shootings, bombings and other attacks still occur daily.

More than 30 bombs struck cities and towns across Iraq on Tuesday, killing at least 52 people and wounding about 250. It was the bloodiest day in nearly a month.