The Karachi police said all four attackers had been gunned down in a foiled attack, and that the building housing the stock exchange had now been cleared.
Two security guards and a police officer also died in the encounter with the attackers, police said.
“The terrorists were four in number and they were armed with weapons and explosives,” a Pakistani security official told NBC News on condition of anonymity, as he was not authorized to speak to the media about the attack. "They entered the stock exchange building in the morning and killed two security guards at the main entrance."
The official said there were few people inside the building at the time of the incident as the attackers arrived early in the morning.
Rizwan Ahmend, a police official at the scene, told the Associated Press that, after the attack was over, food supplies were found on the bodies of the gunmen, indicating they may have planned a long siege, which police quickly thwarted.
Mohammad Ayaz Khan, who was trapped inside the stock exchange building during the attack, told NBC News he had just entered his office when he heard gunshots.
“I had no idea what’s going on, but then received a phone call from my boss and he told me about the attack in the stock exchange building,” Khan said, adding that he and two other people had to hide out inside a locked office until police cleared the building.
There were no reports of any wounded among the brokers and employees inside the exchange.
The Karachi stock exchange is Pakistan’s largest and oldest stock exchange. The building that houses it is located in the heart of Karachi's financial district, where the Pakistan State Bank is based, as well as the headquarters of several national and international financial institutions.
Managing director of Pakistan Stock Exchange, Farrukh Khan, said trading continued during the attack.
The Associated Press reported that the Baluchistan Liberation Army claimed responsibility for the attack. NBC News has not been able to independently verify that information.
The group has been waging an insurgency for years, demanding independence for Pakistan’s gas-rich southwestern Baluchistan province, which borders the southern Sindh province, where Karachi is the provincial capital.
The group has also circulated a photograph of four men in full body armor and camouflage outfits, saying they were the militants who attacked the stock exchange, according to the Associated Press.
Mushtaq Yusufzai reported from Peshawar, Pakistan. Yuliya Talmazan from London. The Associated Press contributed to this report.