Shots can be heard in videos shared on social media.
At least three people are reported to have been injured in the attack.
Four suspects have been killed, police said.
Karachi police chief Ghulam Nabi Memon said: “Four attackers have been killed, they had come in a silver Corolla car.”
Abid Ali Habib, director of Pakistan Stock Exchange, told Geo TV: “An unfortunate incident took place at the Pakistan Stock Exchange.
“They made their way from our parking area and opened fire on everyone.”
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