At least over 10 policemen were reportedly killed in the blast.

Ambulances park at the blast site in southern Pakistani port city of Karachi on Nov. 11, 2010. At least 30 people were killed and 150 others injured in a powerful blast that went off Thursday night in the downtown area of Karachi, the largest industrial city in southern Pakistan. [Arshad/Xinhua]

The blast was just so huge that it had left a 10-feet-deep crater on the blast site and all the nearby buildings were seriously damaged, said an eyewitness.

Police sources said that the blast was caused by an explosive- laden truck.

Police have rushed to the scene and sealed off the area shortly after the blast. Rescue work is under way. A lot of ambulances are seeing coming in and out the area, said the sources in Karachi.

At least 40 injured people were admitted into the Civil Hospital in Karachi while some 20 others were hospitalized at Jinnah Hospital in the city, said hospital sources, adding many injured were in critical condition.

Pakistan Taliban (TTP) has claimed the responsibility for the attack immediately after the blast was reported. It also threatened that the next target of attack is the Pakistani president's house.

Thursday night's attack is the second most serious incident of its kind over the last six months in Karachi. Not long before a shrine in Karachi was attacked by a blast, which left over a dozen of people killed and many others injured.