A powerful bomb in the center of Pakistan's largest city leveled a police building Thursday, killing at least five people and wounding 40, police and witnesses said.

The blast hit the headquarters of the Crime Investigation Department in Karachi, said police officer Iqbal Mahmood.

An Associated Press photographer at the scene said there was a 10-feet (3 meter) wide crater outside the several-story building, which was destroyed. The size of crater suggested it was a vehicle bomb.

The building was in a high security part of the city, not far from the heavily fortified U.S. consulate, two luxury hotels and government buildings, including the governor and the chief minister's residences.

TV footage showed bloodied victims leaving the scene and security officers searching through the debris of the police building.

Dr. Seemi Jamai said five bodies had been brought to a nearby hospital, along with 40 injured.

Pakistan is battling Islamist militants with links to al-Qaida that are trying to overthrow the U.S.-allied government.

The insurgents have repeatedly bombed government, police and Western targets over the last three years.