Among the dead were police and security personnel, said Mohammed Azim, a senior local volunteer who runs the Eid Rescue Center.
Azeem said rescue and paramilitary security personnel were on the scene of the ongoing operation.
The video shows security and barricades outside the stock exchange in Karachi, CNN affiliate Geo News said.
Abid Ali, director of Pakistan Stock Exchange, told a news conference in Geo News that four attackers entered the compound and opened fire, but were killed by security forces.
“There were four attackers who came from the parking lot. They threw a grenade at the main gate of the KSEE (stock exchange) and then started firing indiscriminately,” Ali said.
“The attackers were wearing uniforms that looked like police uniforms. All four were killed and the situation is currently under control.”
The tweet read: “We will provide a more detailed statement once the situation is under control and more details are available. At the moment there are fires and reinforcements.”
The Pakistan Stock Exchange administration sent a message that the “Rangers” had entered the compound and that “four terrorists” had died.
The administration told workers inside the building to stay on the high floors and “let the Rangers blend in and then let everyone out in a systematic manner.”
Pakistan Stock Exchange in Karachi is the largest in the country. It is located in the financial center of the city, where all the major banks and financial services are located and usually has a large security presence.
This is a developing story.