Militants have attacked a police compound in the heart of Pakistan's largest city with a hail of gunfire and a massive car bomb, levelling the building and killing at least 15 people.
The gang of around six gunmen managed to penetrate a high-security area of Karachi that is home to the US Consulate, two luxury hotels and the offices of regional leaders.
While no stranger to extremist violence, Karachi has not witnessed this kind of organised assault in recent years.
It was the first major attack against a government target outside the northwestern tribal regions for several months, showing the reach of Islamist militants seeking to overthrow the US-allied government despite efforts to crack down on them over the last three years.
The gunmen first opened fire on the offices of the Crime Investigation Department (CID) before detonating a huge car bomb, said Sindh Home Minister Zulfiqar Mirza.
The building has a detention facility that was believed to be holding criminals and possibly militants. The CID takes the lead in tracking down militants in Karachi.
Earlier this week, the agency arrested six members of Lashkar-e-Jhangvi, an al-Qaida linked group blamed for several high profile attacks in recent years. The suspects appeared before a court earlier on Thursday.
The blast could be heard several miles away in the city of 14 million people. It destroyed much of the multi-storey police building, damaged nearby houses and left a three-metre wide crater in the road.