At least three people have been killed after gunmen attacked the Pakistan Stock Exchange on Monday morning.
Two security guards and a policeman died in the incident, which Pakistan police have declared a terrorist attack.
The four gunmen have now been shot dead by officers.
Officers said militants surrounded the building and opened fire at the entrance in Karachi.
Inside the stock exchange, broker Yaqub Memon told reporters how he and his colleagues were huddled inside their offices.
As the firing ended and the gunmen were killed, Mr Memon said police gathered all the employees and brokers in a single room while security forces checked each floor to ensure there were no explosives.
There were no reports of any wounded among the brokers and employees inside the exchange.
Heavily armed special forces quickly surrounded the building located in the heart of Karachi’s financial district, where the Pakistan State Bank is located, as well as the headquarters of several national and international financial institutions.
Local television stations broadcast images of police in full body armour surrounding the building.
Rizwan Ahmend, a police official at the scene, said that after the attack was over, food supplies were found on the bodies of the gunmen, indicating they may have planned a long siege.
A militant group from a neighbouring province, the Baluchistan Liberation Army, said it carried out the attack.
The group has been behind a series of attacks in Karachi in recent years, including on the Chinese Consulate in November 2018 in which two people were killed.
The Karachi stock exchange is Pakistan’s largest and oldest, incorporated today with the exchanges in Islamabad and Lahore.