A car bomb ripped through a police bus in central Istanbul during the morning rush hour on Tuesday, killing 11 people and wounding 36 near the main tourist district, a major university and the mayor's office.

The car was detonated as police buses passed, Istanbul Governor Vasip Sahin told reporters, in the fourth major bombing in Turkey's biggest city this year. There was no immediate claim of responsibility but Kurdish militants have staged similar attacks, including one last month in Istanbul.

"A car-bomb attack was made against vehicles carrying our rapid-response police and passing by on the road, resulting in seven police and four civilians losing their lives," Sahin said. "Three of the 36 wounded were in critical condition,"  he added.

The blast hit the Vezneciler district, between the headquarters of the local municipality and the campus of Istanbul University, not far from the city's historic heart. It shattered shop windows and scattered rubble over nearby streets.

"There was a loud bang, we thought it was lightning but right at that second the windows of the shop came down. It was extremely scary," said Cevher, a shopkeeper who declined to give his surname. The blast was strong enough to topple all the goods from the shelves of his store.

The police bus that appeared to have borne the brunt of the blast was tipped onto its roof on the side of the road. A second police bus was also damaged. The charred wreckage of several other vehicles lined the street. Gunshots were heard in the area after the blast.

Turkey has suffered a spate of bombings this year, including two suicide attacks in tourist areas of Istanbul blamed on Islamic State, and two car bombings in the capital, Ankara, which were claimed by a Kurdish militant group.

The outlawed Kurdistan Workers Party (PKK) claimed responsibility for a May 12 car bomb attack in Istanbul that wounded seven people. In that attack, a parked car was also blown up as a bus carrying security force personnel passed by.

The PKK, which has waged an armed insurgency against the Turkish state since 1984, frequently targets passing police and military vehicles with remote-controlled car bombs in its attacks in the largely Kurdish southeast

Source: KUNA