A huge bomb explosion ripped through a multi-storey building housing international businesses in the southern Pakistani port of Karachi Friday, killing two people and injuring four others, Pakistani police said. "It was a bomb explosion and the device was placed near a pillar at the entrance to the 12-storey plaza," said police officer Ajmal Magsi. Two people were killed, he said, adding that four others were injured by flying shards of glass. "None of them was seriously wounded." Police chief of operations in Karachi Tariq Jamil described the bombing as a "terrorist act". "But it will be premature to speculate who could be behind the explosion and the motives." The timed device contained 500 grams of explosives, bomb disposal unit official Mohammad Iqbal said. The blast occurred before staff began arriving at work in the glass panelled building, which houses 120 business offices and is located on the main Sharae Faisal route to the busy Quaid-e-Azam International airport. A security guard, who was asleep inside the building when the explosion occured, said he was woken up by "an ear-splitting bang". "I was hit by a piece of glass and I rushed out where I saw another guard lying on the ground motionless," Mohammad Aslam said. Police said the powerful blast hurled a body 100 meters and damaged the first three floors. However, no part of the building collapsed. Staff working in the offices were sent home by police, who closed the building for the day. The explosion came a week after a massive suicide bombing which killed 48 people at a Shiite Muslim mosque at Quetta, capital of southwestern Baluchistan province. **PHOTO CAPTION*** Volunteers and police prepare to retrieve a dead body from the site of a bomb explosion in Karachi, Friday, July 11, 2003. (AP Photo/Shakeel Adil)