At least seven people were killed, including the attackers, when gunmen stormed the Pakistan Stock Exchange building in the financial hub of Karachi.
Police officers at the site said the dead included two security guards, a policeman and the four attackers. Seven others were wounded.
No group has claimed responsibility for the attack yet.
Two gunmen were killed at the gates of the building which is in a high-security zone and houses the head offices of many private banks.
They attacked the gate with grenades and guns. The other two attackers were injured and were killed when they entered the building.
Abid Habib, director of the Pakistan Stock Exchange, was in his office when the attack started.
He told the local media that he was sheltering with 20 other staff members when the paramilitary started clearing the building.
He said the attackers arrived in a car at 10 am (Pakistan time) and forced their way into the complex before randomly firing.
Law enforcement officials cleared the area after gunshots and explosions were heard.
Over 1,000 traders and staff were present in the building when the attacks started, local media reports.